WASHINGTON (Reuters) - President Donald Trump’s call for Congress to toughen the Iran nuclear deal faced opposition on Friday from among the ranks of his fellow Republicans as well as from Democrats, narrowing the chances any legislation could pass.

A man watches a television broadcast of U.S. President Donald Trump's speech, in Tehran, Iran October 13, 2017. Nazanin Tabatabaee Yazdi/TIMA via REUTERS

As Trump announced that he had chosen not to certify Tehran is complying with the deal but would not immediately withdraw from it, Republican Senators Bob Corker and Tom Cotton offered an outline of legislation they said would “address flaws” in the accord.

If passed, the measure would set stricter restrictions on Iran and immediately revive U.S. sanctions imposed over Iran’s nuclear program if Tehran is deemed able to produce a nuclear weapon within a year.

“We have provided a route to overcome deficiencies (in the agreement) and to keep the administration in the deal, and actually make it the kind of deal that it should have been in the first place,” Corker, chairman of the Senate Foreign Relations Committee, said on a call with journalists.

Republicans control Congress, but their four-seat edge in the Senate means any measure would need Democratic support to pass, even if every member of Trump’s party supports it.

That is not a given.

Republican Senator Marco Rubio said he had “serious doubts” about the Corker-Cotton plan. He said he would reserve judgment until the final measure, but preferred that Trump abandon the deal.

“Ultimately, leaving the nuclear deal, reimposing suspended sanctions, and having the president impose additional sanctions would serve our national interest better than a decertified deal that leaves sanctions suspended or a new law that leaves major flaws in that agreement in place,” Rubio said in a statement.

Most Democrats were strongly opposed.

Senator Ben Cardin, ranking Democrat on the Foreign Relations panel, said he would only support a measure backed by European allies who had signed the nuclear pact, formally known as the JCPOA.

“Anything we do must be consistent with the JCPOA, cannot lead us on a path to violate the JCPOA and must have the support of our European allies,” he told Reuters in a telephone interview.

Cardin said he wanted a full-Senate briefing on the plan from administration officials, and then committee hearings.

Corker acknowledged the tough fight ahead, but said he hoped to win over Democrats. He pledged to seek the support of European allies Britain, France and Germany, who had signed the agreement and urged Trump not to decertify.