FURIOUS US Vice-President Joe Biden lashed out at Republican opponents of a nuclear agreement with Iran yesterday, warning they were putting the nation in peril.

Forty-seven Senate Republicans, including several potential 2016 presidential candidates, took the unprecedented step of directly, publicly addressing Iran in a letter intended to scupper the sensitive talks.

“It has come to our attention while observing your nuclear negotiations with our government that you may not fully understand our constitutional system,” the letter said.

It claimed any deal agreed before President Barack Obama left office in 2017 was nothing more than an executive agreement between Mr Obama and Supreme Leader Ali Khamenei.

“The next president could revoke such an agreement with the stroke of a pen and future congresses could modify the terms at any time,” it said.

Mr Biden reacted with anger. 

“The letter sent by 47 Republican Senators to the Islamic Republic of Iran, expressly designed to undercut a sitting president in the midst of sensitive international negotiations, is beneath the dignity of an institution I revere,” he said.

“This letter, in the guise of a constitutional lesson, ignores two centuries of precedent and threatens to undermine the ability of any future US president, whether Democrat or Republican, to negotiate with other nations on behalf of the US,” he said.

Senate Democrat leader Harry Reid added to the complaint, warning against the “unprecedented” intervention in negotiations “with the sole goal of embarrassing the president.”