The head of Ukraine's interior ministry has said that police killed the suspect at a supermarket in Kyiv's Holosiivskyi district.
Ihor Klymenko said special forces entered the store, where the gunman had taken people hostage and shot at police officers, after attempts to make contact with a negotiator failed.
The Security Service of Ukraine (SBU) said later that the incident was being investigated as a terrorist act.
Ukrainian President Volodymyr Zelenskyy said that five people are known to have died.
The mayor of Kyiv, Vitali Klitschko, added that 15 people were injured in the shooting, and said earlier that those injured included a child.
He added at around 5.10pm that a woman in her 30s died in the hospital, bringing the total to six killed.
In an update after 6pm, Mr Zelenskyy said that one of the six killed was a hostage, and four others were killed on the street.
He added on Telegram that investigators are aware that the attacker set fire to the apartment before going out into the street with a weapon.
According to Mr Zelenskyy, the suspect had also been criminally investigated before - although it is unclear what for - was born in Russia, and had lived in the Donetsk region for a long period of time.
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According to the Associated Press, televised footage of the scene showed police taking cover in the shopping mall that housed the supermarket while shots were fired.
Bystanders were escorted away from the scene.
Queen Elizabeth II died aged 96 on 8 September 2022. Her 100th birthday would have taken place on Tuesday.
Set up as one of three projects honouring the Queen's legacy, the independent Queen Elizabeth Trust will offer grants for UK communities to develop and regenerate shared spaces.
It's set to be formally unveiled on Tuesday, along with the National Memorial landmark and gardens in St James's Park, and the Digital Memorial tribute to her life and service.
In support of the new charity, the government will make a one-off £40m endowment to start the projects. These could include developing underused buildings, green spaces and neighbourhood hubs in UK communities.
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Sir Damon Buffini, chair of the Queen Elizabeth Trust, said in a statement: "I'm honoured and excited to have been chosen as the founding Chair of the Queen Elizabeth Trust to help guide its direction from the start.
"This is a real chance to support communities across the United Kingdom and bring shared spaces back to life: places where people of all ages and backgrounds can meet, connect, and belong.
"As an organisation, we're ambitious about what we can achieve, and our goal is to significantly increase our impact by attracting support from others.
"I'm looking forward to rolling up my sleeves, listening and learning from communities, and seeing what we can make happen."
But they did not pass over the information to the prime minister because they were waiting for legal checks on what information could be released, according to a Cabinet Office spokesperson.
Cabinet secretary Antonia Romeo and cabinet office permanent secretary Catherine Little were both present at a meeting between Sir Keir Starmer and senior civil servants on Tuesday night, when the prime minister was finally told about Lord Mandelson's failure to pass vetting.
The spokesperson said: "Senior officials in the Cabinet Office did the right thing and took urgent steps to ensure they could update the prime minister.
"On receipt of the UK security vetting information, the permanent secretary of the Cabinet Office rapidly sought legal and other advice to be in a sound position to share the document, or the fact of it, with the prime minister. She updated the cabinet secretary who agreed with the approach.
"As soon as these checks were conducted, the prime minister was informed."
Sir Keir is fighting to save his premiership as he faces a crunch week over the latest revelations in the vetting row.
Downing Street has blamed Foreign Office officials for clearing the former Labour peer in January 2025 to start as US ambassador, despite him failing the secure vetting process.
The department's chief civil servant Sir Olly Robbins was sacked on Thursday night after Sir Keir and foreign secretary Yvette Cooper lost confidence in him over the scandal.
The prime minister was "not aware" there was a recommendation against giving Lord Mandelson security clearance for the ambassador role - which was overruled by the Foreign Office, according to a document produced by Number 10.
He was only told of the advice on Tuesday.
Sir Keir said he will "set out all the relevant facts in true transparency" to parliament on Monday.
The prime minister on Friday said he was "absolutely furious" and it was "staggering" that he had not been informed the vetting process was overruled to clear Lord Mandelson for the ambassador posting.
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"I was not told that he had failed security vetting, no minister was told... Number 10 wasn't told, that is completely unacceptable," he said.
Criticising officials, the PM said: "It is totally unacceptable that the prime minister making an appointment is not told that security vetting has been failed."
Sir Keir is not resigning or considering his position, No 10 also said on Friday.
David Lammy, who was foreign secretary at the time of Lord Mandelson's appointment, told The Guardian it was "inexplicable" Sir Keir had not been informed of the vetting recommendation and was "shocked and surprised" when he found out what happened last week.
The deputy prime minister, who is now justice secretary, said: "I have absolutely no doubt at all, knowing the PM as I do, that had he known that Peter Mandelson had not passed the vetting, he would never, ever have appointed him ambassador."
Ms Cooper only found out Lord Mandelson failed security vetting on Thursday after being approached by journalists, Sky News understands.
Sir Olly has been invited to speak to the Foreign Affairs Committee as early as next Tuesday.
The committee published correspondence on Saturday showing Ms Cooper had asked the Foreign Office to conduct a "full review" of all the information the department had provided to the committee.
In the letter to the chair, Labour MP Emily Thornberry, the foreign secretary said it was of "paramount importance" the information is "fully accurate".
The opposition party leaders have all called for Sir Keir to resign over the latest revelations, with Kemi Badenoch, for the Conservatives, arguing the prime minister had misled parliament and the public.
SNP Westminster leader Stephen Flynn called on the prime minister to "do the decent thing and resign".
He suggested Sir Keir is "either incompetent, gullible or a liar".
Lord Mandelson was sacked from his Washington role last September when more details emerged about his relationship with Jeffrey Epstein, who died in 2019.
The ex-Labour cabinet minister has previously denied any wrongdoing over his relationship with the paedophile financier and has apologised to Epstein's victims.
Sir Keir was already facing heavy criticism over the decision to hand Lord Mandelson the position, despite it being known that his dealings with Epstein continued after the billionaire's conviction for child sex offences.
"Today's order will ensure that people suffering from debilitating symptoms might finally have a chance to reclaim their lives and lead a happier life," the US president said in the White House on Saturday.
Mr Trump also said his directive will help "dramatically accelerate" access to research and treatments on psychedelic drugs, adding: "If these turn out to be as good as people are saying, it's going to have a tremendous impact."
He made the remarks in front of podcaster Joe Rogan and US military veteran Marcus Luttrell.
Rogan told reporters that he texted Mr Trump about ibogaine as a treatment for depression and PTSD, to which he responded: "Sounds great. Do you want FDA approval? Let's do it."
Mr Luttrell added to the president: "You're going to save a lot of lives through it. It absolutely changed my life for the better."
Ibogaine is made from a shrub native to West Africa. In high doses, ibogaine can cause hallucinations. It's also been linked to cardiac-related deaths.
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Ibogaine is heavily restricted in the UK under the Psychoactive Substances Act 2016, making it a criminal offence to produce and supply it.
US veterans have reported benefiting from the drug after travelling to clinics in Mexico that administer it.
Officers are still investigating whether they are connected to a video posted by an Iran-linked Islamist group claiming to have targeted the building with drones carrying dangerous substances.
The Metropolitan Police said the embassy was not attacked, but closed nearby Kensington Gardens and deployed specialists, some wearing protective clothing.
Confirming the park had been reopened on Saturday, the force said suspicious items had been discovered, including two jars containing a powdered substance.
But police said they had not identified any harmful or hazardous substances so there is no risk to the public and the search has concluded.
Commander Helen Flanagan, of Counter Terrorism Policing London, said: "We recognise this incident and consequent police activity may have caused concern among local residents and the wider public.
"We are grateful to them for their understanding while our work was undertaken.
"Although the items found have been assessed as being non-hazardous, we continue to investigate whether they may have any link to the online video."
A video, which appears to have been shared by the group Harakat Ashab al-Yamin al-Islamia, shows a target over an image of the Israeli embassy and people dressed in hazmat suits flying drones.
The group, which is suspected of being Iran-backed, has also claimed responsibility for other arson attacks in north London, although police say they are not currently treating the incidents as linked.
Counter-terror police are investigating another arson attack on a building that used to belong to a Jewish charity in Hendon, northwest London on Friday night.