The United States will "confront aggressively" Iran's bid to expand its influence across the Middle East even if a nuclear deal is reached, a State Department official said Tuesday.

The official's comments came as Israeli Prime Minister Benjamin Netanyahu, in a controversial address to the U.S.Congress, sought to highlight Iran's expansionist hopes as one reason to halt the nuclear talks.

Top U.S.diplomat John Kerry will travel to Saudi Arabia on Wednesday to reassure U.S.Gulf allies that an Iran deal would not mean Washington would turn a blind eye to the Islamic Republic's regional ambitions.

"Regardless of what happens in the nuclear file, we will continue to confront aggressively Iranian expansion in the region and Iranian aggressiveness in the region," the official said.

Iran, a Shiite Muslim nation, is blamed for helping to prop up Syrian President Bashar al-Assad, for supporting Huthi Shiite rebels who have seized the Yemeni capital and for trying to influence Iraqi leaders.

"You can't read into the nuclear negotiation any kind of determination of where the U.S.relationship with Iran may go in the future," the senior State Department official told reporters.

He said Washington was working closely with its majority Sunni Muslim Gulf allies to help build up their security and capabilities to defend their interests.

"Obviously the Gulf states are watching the negotiations very carefully, they have a legitimate reason to want to understand better what it is we're trying to achieve."

But he stressed: "This is not going to change any of the other aspects of our approach to Iran."

Netanyahu said in his controversial address to the U.S.Congress on Tuesday that "at a time when many hope that Iran will join the community of nations, Iran is busy gobbling up the nations.

"We must stand together to stop Iran's march of terror," he said to applause. (AFP)