US President Barack Obama said he is "embarrassed" for the 47 Republican senators who signed a letter to Iran on a possible nuclear deal earlier this week.
"I'm embarrassed for them. For them to address a letter to (Iran)… and their basic argument to them is 'don't deal with our president ‘cause you can't trust him to follow through on agreement," Obama said in a trailer for a Vice News interview scheduled to run in full on Monday, Politico reported on Friday.
Germany's foreign minister had also hit out at the senators on Thursday, saying the letter could undermine Tehran's confidence in the negotiations at a critical juncture.
"This is not just an issue of American domestic politics, but it affects the negotiations we are holding in (Switzerland)," Steinmeier told journalists in Washington before meeting lawmakers on Capitol Hill, AFP reported.
"Obviously mistrust is growing... on the Iranian side if we are really serious with the negotiations."
Steinmeier added it would be good "if the letter of the 47 senators no longer causes any disturbance in the negotiations."
In the letter to Iran, the Republicans warned that any deal agreed before Obama leaves office in 2017 is "nothing more than an executive agreement" that could be struck down later by Congress or a future president.
The German foreign minister complained that the move, which has been condemned by US Vice President Joe Biden and several Democratic congressional leaders, could jeopardize the Western position in the nuclear talks. The letter allows Iran to cast doubt on the West's credibility, Steinmeier said at an event organized by the Center for Strategic and International Studies, a Washington think tank.
"This is not a trifle," he stressed. "The negotiations are difficult enough, so we didn't actually need further irritations."
