US President Joe Biden has slammed Republicans for blocking an emergency budget bill that includes aid to Ukraine, saying failure to support the country is "close to criminal neglect."

Biden met German Chancellor Olaf Scholz at the White House on Friday.

Scholz called for a swift decision on US aid for Ukraine, saying that without the support of the United States and European states, Ukraine will have no chance to defend itself.

Biden said the failure of the US Congress to back Ukraine would be "close to criminal neglect" and "outrageous."

A bipartisan group of senators had put together a package including security measures for the border with Mexico and wartime aid to Ukraine and Israel.

But most Republicans voted against advancing it in the chamber on Wednesday, after former President Donald Trump, who is seeking re-election in the presidential race this year, urged them not to compromise.

Prospects for new US aid to Ukraine remain unclear. The Senate is now discussing a new emergency budget bill that does not include the border security measures that Trump called insufficient.