Republican senators pressure Biden to transfer fighter jets to Ukraine

Pressure is mounting on US President Joe Biden to bolster Ukraine's defences after his administration quashed Poland's offer to send fighter jets with US help.

More than 40 Republican senators have written an open letter in which they say they "strongly disagree" with Biden's stance.

They have now called on him to immediately "facilitate the transfer of aircraft and air defence systems".

The White House says it's "high risk".

Poland surprised the US administration this week when it offered to deploy MiG-29 jets to a US military facility in Germany "immediately and free of charge", ready for transferring them to Ukraine.

The offer was rejected as "not tenable" by US officials, but the Republican senators disagree.

Their letter reads: "We cannot allow Putin to gain an advantage because of a failure to provide the Ukrainians with needed weaponry, ammunition, communications equipment and medical supplies.

"Supporting Ukraine's fight for freedom against the tyrannical, lawless Russian invasion of Ukraine's sovereign territory is among the most urgent missions the West has faced in a generation."

The letter is led by Iowa senator Joni Ernst and Utah's Mitt Romney - and includes signatures from most of their Republican Senate colleagues, including minority leader Mitch McConnell.

"We implore you to direct your Department of Defense to facilitate the transfer of aircraft, air defence systems, and other capabilities by and through our Nato partners immediately," it says.

The Pentagon has so far ruled out sending its Patriot missile defence system to Ukraine, but has instead directed two of the units to Poland.

The US is wary of sending military aid directly into Ukraine as Russia could interpret that as a more direct involvement in the war that could escalate the conflict beyond Ukraine.

Nations have preferred to respond to Russia's invasion with sweeping sanctions.