US President Joe Biden announced $1 billion in new security help and the deployment of longer-range weapons and drones to Ukraine on Wednesday -- assuring the ally of America's "unprecedented" support in its war with Russia.

The cash, approved as Russian forces close in on Ukraine's besieged capital Kyiv, includes $200 million allocated over the weekend and $800 million in new funds from an aid package approved last week by Congress.

"These are direct transfers of equipment from our Department of Defense to the Ukrainian military to help them as they fight against this invasion," said Biden, who also announced US help for Ukraine to acquire "additional longer-range anti-aircraft systems."

As expected, Biden gave no ground on the notion of a Western-imposed no-fly zone over the ex-Soviet state, which NATO has consistently rejected for fear of an escalation that could bring the alliance into direct conflict with Russian forces.

Ramping up its military assistance instead, the White House said Ukraine will receive an additional 800 Stinger anti-aircraft systems, 9,000 anti-tank weapons, 7,000 light weapons and 20 million rounds of ammunition.

And the United States will be providing Ukraine with 100 drones -- or Tactical Unmanned Aerial Systems -- which Biden said "demonstrates our commitment to sending our most cutting-edge systems to Ukraine for its defense."

Concerning the deployment of longer-range systems, Gregory Meeks, the chairman of the House Foreign Affairs Committee, indicated the weapons involved would be Soviet-made S-300 surface-to-air missile systems.

"These S-300s and longer-range artillery forces is what will help close the sky" over Ukraine, Meeks said on CNN following Biden's address.

"President Zelensky is not asking for American troops or American equipment or anything of that nature to close the skies," Meeks said. "What he's asking for is the artillery that will do that. The S-300 may be the one that does that."