By Makini Brice and Richard Cowan
WASHINGTON (Reuters) -The U.S. Senate will not vote on a package to provide more aid to Ukraine and bolster U.S. border security before early next year, as Democratic and Republican negotiators continue their work, chamber leaders said on Tuesday.
"Our negotiators are going to be working very, very diligently over the December and January break period, and our goal is to get something done as soon as we get back," Senate Democratic Leader Chuck Schumer told reporters.
The chamber's No. 2 Republican, John Thune, also said a deal would not be reached before January. "Democrats have run out the clock to the point where getting a substantive border security deal passed before Christmas is impossible," he said on the Senate floor.
In a joint statement, Schumer and Senate Republican leader Mitch McConnell said negotiators "are making encouraging progress" but "challenging issues remain."
The White House has warned that by the end of the year U.S. aid will run out to help Ukraine retake territory occupied by Russia since the 2022 invasion.
The Biden administration's request for another $61 billion in support has been bogged down in Congress, where Republicans say it must be paired with tougher immigration controls along the U.S.-Mexico border. Funding for Israel, another element of the package, is less controversial.
Immigration is one of the most divisive issues in U.S. politics and bipartisan reform attempts have repeatedly failed over the past 20 years.
"I cannot state how complex this is. It's the most complicated area of American law," said Senator Kyrsten Sinema, an independent involved in the talks.
Ukrainian President Volodymyr Zelenskiy faced a skeptical reception from Republicans when he visited Washington last week to drum up support.
It is not clear that any deal reached in the Democratic-majority Senate will win support in the Republican-controlled House of Representatives, where a significant number of party hardliners oppose providing additional funding to Ukraine.
January also marks the start of the state-by-state Republican presidential nominating contest and lawmakers will face a deadline to avoid a partial government shutdown.