Republican senators opened the way for a new showdown with Barack Obama on Tuesday, after an apparently disastrous meeting with UN ambassador Susan Rice that had been widely seen as an attempt to smooth her path to nomination as US secretary of state.

The meeting on Capitol Hill had been expected to end in rapprochement after one of Rice's leading Senate critics, John McCain, stepped back from a bitter row over the 11 September attack on the US consulate in Benghazi.

But McCain and his colleagues emerged from the 90-minute private encounter to say they were "significantly troubled" by Rice's explanation of her earlier accounts of the attack on the US mission