Senate leader expects strong debate over Iran bill amendments

"I still expect to see a vigorous debate this week. I still expect to see a robust amendment process," McConnell said in a Senate speech before debate on the bill began on Tuesday.

The Senate Foreign Relations Committee voted 19-0 last week for a compromise version of the Iran Nuclear Review Act in a rare display of bipartisan unity in the deeply divided Congress.

But some U.S. Republicans have introduced amendments seeking to toughen the bill, raising the possibility of a partisan battle that could complicate the measure's chances of passing. Many Republicans worry that Democratic President Barack Obama is so eager to reach a nuclear agreement with Iran that he will allow the Tehran government to develop a nuclear weapon.

Before the compromise, Obama had threatened to veto the bill, saying that some of its provisions threatened delicate international negotiations with Iran.

(Reporting by Patricia Zengerle; Editing by Susan Heavey and Bill Trott)