WASHINGTON (Reuters) - U.S. Senator Bob Corker, the Republican chairman of the Senate Foreign Relations Committee, urged President Donald Trump’s administration on Monday to work closely with European allies as it develops its new Iran policy.

Sen. Bob Corker (R-TN) speaks with reporters after announcing his retirement at the conclusion of his term on Capitol Hill in Washington, U.S., September 26, 2017. REUTERS/Aaron P. Bernstein

“This is something that can only work if the administration exercises tremendous diplomacy with our European allies,” Corker told reporters as the Senate returned to the Capitol for the first time since Trump announced his Iran policy.

Trump defied both allies and adversaries on Friday by refusing to certify that Iran is complying with an international agreement on its nuclear program, and threatened that he might ultimately terminate the accord.

Corker is leading an effort in Congress to write legislation setting new conditions for the U.S. role in the pact, such as automatically reimposing sanctions if Iran is deemed to be within one year of developing a nuclear weapon.

Details have not been finalized, but the plan’s outline raised concerns that it might cause Washington - not Tehran - to violate the deal reached with Britain, France, Germany, Russia, China, Iran and the European Union.

Corker said Democratic senators told him that Washington must work with Europe.

Trump’s fellow Republicans control the Senate and House of Representatives, but their Senate majority is so narrow that most legislation needs Democratic votes to pass.

European Union foreign ministers meeting in Luxembourg on Monday reaffirmed their support for the nuclear pact and said failure to uphold it could have serious consequences for regional peace, and undermine efforts to check North Korea’s nuclear ambitions.

Corker said he had tried to convince European officials that the news on Iran was not all bad.

“I ... shared with them that, look, if I were them, I’d look at this as ‘the glass is half full,’ he didn’t withdraw from the JCPOA (the nuclear deal), and that’s step one,” Corker said.

He described efforts under way in Washington as a chance to address “deficiencies” in the nuclear pact, in which Iran agreed to curb its nuclear ambitions in exchange for sanctions relief.

Every Republican in Congress, as well as some Democrats, opposed the accord when it was reached by former Democratic Barack Obama’s administration in 2015.

Corker and Republican Senator Tom Cotton, who worked with him on the legislation, met later on Monday on Iran with Senate Majority Leader Mitch McConnell.