The top Republican in Congress, in his first formal speech since taking the speaker's gavel in October, said a deal taking shape in the Senate does not go far enough to prevent migrants from entering the country along the U.S.-Mexico border.

"From what we've heard, this so-called deal does not include transformational policy changes needed to actually stop the border catastrophe," he said in prepared excerpts of his remarks on the House floor.

Johnson's remarks made clear that any bipartisan compromise to emerge from the Democratic-majority Senate would face a difficult reception in the House, which his Republicans control by a 219-213 margin.

Donald Trump, the frontrunner for the Republican presidential nomination, has called on lawmakers to reject any deal ahead of the November elections that will determine control of the White House and Congress.

That would leave emergency aid to Ukraine and Israel in doubt, as House Republicans have said that they will not sign off on more money absent tighter border controls. They are also advancing an impeachment effort of Biden's top border official, Homeland Security Secretary Alejandro Mayorkas, though they are unlikely to succeed in persuading the Senate to remove him from office.

Biden's administration has struggled to cope with record numbers of migrants seeking asylum along the U.S.-Mexico border, and opinion polls show that immigration is a top concern of voters.

Johnson cast the issue in apocalyptic terms, claiming that illegal immigrants have displaced children from classrooms and veterans from retirement homes.

He said Biden already has the authority he needs to prevent unauthorized entry into the country, even if Congress does not tighten existing laws or provide more resources for enforcement.

No. 2 Senate Republican John Thune said party leaders hope to get a clearer idea of where Republican lawmakers stand on a border deal during a meeting on Wednesday.

"The complicating factor of the message is coming out of the House," Thune told reporters. "That's a factor, obviously, that we'll have to take into consideration."

Asked what could lie ahead for aid to U.S. allies including Ukraine and Israel if the effort to craft a border deal fails, Thune said: "They are multiple components to this. And so, my assumption is that there'll be an effort to pass something out of here. What all the individual components are remains to be seen."

(Reporting by David Morgan and Andy Sullivan; Editing by Scott Malone and Mark Porter)

By David Morgan and Andy Sullivan