US President Joe Biden has announced an additional $US800 million ($A1.1 billion) security assistance package for Ukraine to further shore up support for the embattled European country as it faces a fresh onslaught by Russia on its eastern flank.
Addressing the public from the White House's Roosevelt Room, Biden pledged to send dozens of howitzers, 144,000 rounds of ammunition and tactical drones as he called on Congress for supplemental funding to provide additional aid for Ukraine.
"We're in a critical window now of time where they're going to set the stage for the next phase of this war," Biden said.
The United States and allies are "moving as fast as possible" to provide Ukraine with the equipment and weapons it needs.
The US House of Representatives will consider the additional aid for Ukraine as soon as next week, Speaker Nancy Pelosi told reporters.
There is strong support among Democrats and Republicans for assisting Ukraine.
The president also announced plans to ban Russian-affiliated ships from US borders, further ratcheting up pressure on officials in Moscow.
The new arms package is the same size as an $US800 million one announced last week but details are still being worked out, a US official, speaking on condition of anonymity, told Reuters earlier.
On Wednesday, Biden convened US military leaders in an annual White House gathering that took on special significance as the war enters a risky new phase.
Opening the meeting, Biden touted the toughness of the Ukrainian military and said that NATO's unity had shocked Russian President Vladimir Putin.
Russia has said it has entered a new stage of its operation and is methodically seeking to "liberate" the Donbas region of eastern Ukraine.
US officials anticipate Russia's campaign could last many months, grind to a stalemate and test the battlefield capabilities of Ukrainian fighters.
Russia says it launched what it calls a "special military operation" on February 24 to demilitarise and "denazify" Ukraine.
Ukraine and its allies reject that as a false pretext.
US forces are not fighting in Ukraine but are indirectly engaged, arming, training and financing its forces.
The US aid announced last week included artillery systems, artillery rounds, armoured personnel carriers and unmanned coastal defence boats, broadening the scope of material sent to Ukraine to include new types of heavy equipment.
Adding this week's package brings total US military aid to Ukraine since Russia invaded to more than $US3 billion.
Following his announcement, Biden will fly to the Pacific northwest for a two-day trip to promote his domestic agenda.