Legislation that would provide billions of dollars in new US security assistance for Ukraine and Israel has been blocked in the Senate as Republicans pressed their demands for tougher measures to control immigration at the border with Mexico.
As voting continued on Wednesday, the vote was 45 in favour to 48 against, meaning the $US110.5 billion ($A168 billion) measure could not obtain the 60 votes needed in the 100-member Senate to pave the way to start debate on the bill.
The vote was along party lines, with every Senate Republican voting no along with Senator Bernie Sanders, an independent who generally votes with Democrats but had expressed concerns about funding Israel's "current inhumane military strategy" against Palestinians.
"Today's vote is what it takes for the Democratic leader to recognise that Senate Republicans mean what we say. Then let's vote. And then let's finally start meeting America's national security priorities, including right here at home," Senate Republican Leader Mitch McConnell said in a floor speech earlier on Wednesday.
Australian Associated Press