US Secretary of State Antony Blinken on Thursday spoke to key ally Poland on ways to support Ukraine as Russian attacks and upcoming US elections raise new jitters.

The top US diplomat opened talks with Poland's leadership in Warsaw after an overnight train ride from Ukraine, where he paid a rare joint solidarity trip with Britain's new foreign secretary, David Lammy.

Blinken promised a quick review of Ukraine's request for permission to fire Western weapons deeper into Moscow, whose alleged acquisition of new short-range Iranian missiles is expected to free up its arsenal for more strikes.

He will also likely discuss an appeal Wednesday by Ukrainian Foreign Minister Andriy Sybiga for neighbouring countries to help shoot down missiles over its western region.

President Joe Biden -- who has been hesitant to take actions that risk triggering direct conflict between nuclear-armed Russia and the United States -- will review the Ukrainian requests Friday in a White House meeting with British Prime Minister Keir Starmer.

Russia has cast Western help for Ukraine as further justification for its 2022 invasion of the former Soviet republic, which had been tilting toward the West.

"We haven't a doubt that the decision to lift restrictions on long-range weapons to attack the Russian Federation's territory was taken long ago," Foreign Minister Sergei Lavrov said Thursday.

Poland united on Ukraine

Blinken will meet separately in Warsaw with Prime Minister Donald Tusk and President Andrzej Duda, bitter rivals on the direction of the European Union member.

While split on domestic policy, Poland, with its dark historical memories of Moscow, has shown unity in backing Ukraine since its invasion by Russia in 2022.

Poland has ramped up purchases of US weapons since the war, last month signing a deal with Boeing to buy 96 Apache attack helicopters for $10 billion.

Blinken hopes to use the final months of Biden's administration to work with allies to ensure broad and sustained support for Ukraine, which has received billions of dollars in Western military and economic support.

The November 5 US election could dramatically shift the stance of Ukraine's biggest backer, however, with Republican candidate Donald Trump declining to say in a debate on Tuesday whether he wants Ukraine to win.

Biden's political heir Kamala Harris referenced Poland -- and the Polish-American vote in the politically crucial state of Pennsylvania -- as she vowed to keep up the fight for Ukraine.

If the United States had not backed Ukraine, Russian President Vladimir Putin "would be sitting in Kyiv with his eyes on the rest of Europe", Harris said.

"Why don't you tell the 800,000 Polish-Americans right here in Pennsylvania how quickly you would give up for the sake of favour, and what you think is a friendship with what is known to be a dictator who would eat you for lunch?" she told Trump, referring to his past statements of admiration for Putin.

Poland, since the end of the Cold War an enthusiastic US ally, nonetheless sought to work with Trump during his 2017-2021 presidency.

Duda met with Trump in April in New York, and the two have praised each other's records.

The more European-oriented Tusk, who triumphed in elections last year, has sought to bolster Poland's democratic institutions that had been undermined by the previous Duda-aligned government.

Biden this year welcomed Tusk and Duda jointly at the White House, hoping to send a signal of bipartisanship on Ukraine.

Tusk has not shied away from calling out members of Trump's Republican Party who oppose assisting Ukraine. 

During a long delay in Congress approving new military aid to Ukraine, Tusk said that Republican House Speaker Mike Johnson bore personal responsibility for "thousands of lives".