The fates of US military aid to Ukraine as it fights Russia's invasion and the politically explosive issue of illegal immigration into the United States were up in the air Friday as President Joe Biden rebuked congressional Republicans for stalling on a deal.

The Republican speaker of the House of Representatives said Congress is not ready to approve renewal of US military aid crucial to Ukraine for its desperate fight against Russian invasion, because there is no parallel deal on reinforcing the US-Mexican border -- a major conduit for undocumented migrants.

The Senate "appears unable to reach any agreement," wrote Speaker Mike Johnson in a letter to lawmakers, adding that in any case his party would not give approval in the House, meaning it "would have been dead on arrival."

But Biden responded in a statement that Republicans and Democrats have in fact been working intensively on a bipartisan deal to address those border security issues.

"What's been negotiated would -- if passed into law -- be the toughest and fairest set of reforms to secure the border we've ever had in our country," he said in a statement. "If you're serious about the border crisis, pass a bipartisan bill and I will sign it."

"It would give me, as president, a new emergency authority to shut down the border when it becomes overwhelmed. And if given that authority, I would use it the day I sign the bill into law," he said.

The bipartisan deal had advanced in the Senate in recent days. It would couple massive new aid for pro-Western Ukraine's military -- soon entering its third year of fighting off President Vladimir Putin's invasion -- and wide-ranging reforms to US immigration policy, including more ability to seal the porous southern border.

But the complex negotiations now appear to have collapsed.

This follows lobbying by Donald Trump, the former president and likely Republican nominee to contest the November presidential election.

Trump, who has questioned the US support for Ukraine's war effort, has placed fear over illegal immigration at the heart of his platform.

This week he called the extensive border reforms being negotiated "meaningless," although senior Republicans had previously praised the proposed measures as the toughest new restrictions on border crossings in years.

Democrats narrowly control the Senate, while Republicans have their own slim majority in the House, with far-right Trump allies holding the balance of power there.

Johnson said Biden was responsible for a "border catastrophe" and said Republicans would seek to remove Homeland Security Secretary Alejandro Mayorkas in an impeachment process starting next week.

A vote on impeaching Mayorkas will be held "as soon as possible," Johnson wrote. 

The Democratic-controlled Senate will all but certainly acquit Mayorkas, meaning he will not be forced from his job, which includes responsibility for border security.