Biden said the newest round of US support will include heavy artillery, dozens of howitzers, 144,000 rounds of ammunition for them, and tactical drones.

He said the new package was tailored to help Ukraine's forces address the growing Russian offensive in the country's east, which he said would be a different kind of fight than that in the north around Kyiv, where Ukrainian forces successfully beat the Russian invasion back in the first six weeks of the war.

"We're in a critical window now of time where that they're going to set the stage for the next phase of this war. And the United States and our allies and partners are moving as fast as possible to continue to provide Ukraine ... the weapons their forces need to defend their nation."

Biden also announced that Russia-affiliated ships would be banned from US ports, and that the US Treasury was putting up a fresh $500 million for Ukraine's government so it can pay salaries and pensions and provide services.

He said the unity between the US and allies in support of Ukraine is sending "an unmistakable message" to Russian President Vladimir Putin.

"He will never succeed in dominating and occupying all of Ukraine. That will not happen," Biden said.

Biden pledged that US military aid for Kyiv will not dry up, and said he was preparing to ask Congress for more funds "to keep weapons and ammunition flowing without interruption."

He called on allies to continue their support.

"We have the capacity to do this for a long time. The question is, are we going to maintain the support of the international community to keep the pressure on Putin" and keep enforcing tough sanctions on Russia, he said.

"The most important thing is maintain unity," he said.