Biden set to deliver $800 mn in new security aid to Ukraine: US official

US President Joe Biden will announce $800 million in new security assistance to Ukraine Wednesday, a White House official said, with the announcement set to come soon after Ukrainian President Volodymyr Zelensky addresses the US Congress.

The announcement, expected to come at 11.45 am (1545 GMT), brings "the total (aid) announced in the last week alone to $1 billion," the official, who spoke on condition of anonymity late Tuesday, said. 

Zelensky is set to renew his appeals for more aid in his virtual address to Congress early Wednesday, as some US lawmakers press the White House to take a tougher line over Russia's invasion.

Biden had already authorised $200 million in additional military equipment to Ukraine on Saturday. That came on top of $350 million authorised by Washington, also for military equipment, on 26 February -- at the time, the largest such package in US history.

The White House official did not give details on what would be included in the $800 million of security assistance to be announced Wednesday.

But in the past year the US has provided over 600 Stinger missiles and approximately 2,600 Javelin anti-armour systems to Ukraine, along with an assortment of radar systems, helicopters, grenade launchers, guns and ammunition, and other equipment, the official said.

"The US remains by far the largest single donor of security assistance to Ukraine," the official said.

Zelensky's pleas for help to defend his country from Russia's deadly assault have grown increasingly desperate, and he has repeatedly urged Washington, the European Union and NATO for military hardware, including planes, as well as a no-fly zone. 

Biden has ruled out the no-fly zone, warning that it would trigger a catastrophic war with nuclear-armed Russia. 

There is a growing clamour on both sides of Congress, however, for a more assertive US posture. 

Zelensky's speech Wednesday will be his second to members of Congress this month, but will likely be to a much larger audience than his 5 March appearance, when he called for Russian-made planes to be delivered to his air force.