"Though he had contributed to the Times in the past (most recently in 2015), he was not on assignment for any desk at the Times in Ukraine.

"Early reports that he worked for the Times circulated because he was wearing a Times press badge that had been issued for an assignment many years ago."

Mr Nebytov said Mr Renaud was with another journalist who was injured in the shooting and was taken to a hospital in Kyiv.

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Mr Arredondo told Italian journalist Annalisa Camilli, who was at the hospital when he arrived, that he and Mr Renaud were shot as they were approaching a Russian checkpoint just after a bridge in Irpin. The driver turned around but the firing continued, he said.

Speaking just before being taken for surgery after being shot in the lower back, the journalist said his colleague was hit in the neck and remained on the ground while an ambulance brought him to hospital. Mr Renaud was "left behind", he said.

Mr Arredondo added they were filming refugees fleeing the area when they were shot.

'Brazen aggression'

White House national security adviser Jake Sullivan told CBS News the US government would be consulting the Ukrainians to determine how the journalists were shot and said he would "execute appropriate consequences".

"This is part and parcel of what has been a brazen aggression on the part of the Russians, where they have targeted civilians, they have targeted hospitals, they have targeted places of worship, and they have targeted journalists," Mr Sullivan said.

Award-winning sibling duo

Mr Renaud usually worked alongside his brother, Craig Renaud, but it is not known if they were both in Ukraine.

The brothers have worked in several war and conflict zones over the years, including Iraq, Afghanistan, Egypt and Libya.

In 2004 they were embedded with the US Army in Iraq and were filming when a rocket attack struck an American military base in Baghdad, killing four soldiers and severely wounding two others.

They have won several top awards for their work, including a Peabody for a series they made for VICE News on a Chicago school for disruptive students.

The pair have also been nominated for several Emmys.

Their website says they live and work in New York City and Little Rock, Arkansas.

Russian forces try to blockade Kyiv

Kyiv's chief regional administrator, Oleksiy Kuleba, said Russian forces appeared to be trying to blockade and paralyze Kyiv with day and night shelling of the suburbs.

He said Russian agents were in the capital marking out possible future targets.

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Residents of Irpin woke up on Sunday to shooting after heavy shelling overnight. Bodies lay in the open in the streets and a park on Saturday.

Mr Kuleba promised an all-out assault by the Russians would be met by stiff resistance.

"We're getting ready to defend Kyiv, and we're prepared to fight for ourselves," he said.