Iraq's vice-president has added his voice to calls for Prime Minister Ibrahim al-Jaafari to step down as candidate to lead a new government.
Mr Mahdi (left) said Mr Jaafari was losing Shia support
Adel Abdul Mahdi is the most senior figure in Mr Jaafari's dominant Shia alliance to urge him to withdraw.
Mr Jaafari's nomination is one of the main sticking points in deadlocked coalition talks with Kurds and Sunnis.
In further violence, 10 people have been killed in a car bomb attack in the Shia district of Sadr City in Baghdad.
Another 25 people were injured in the explosion that happened during the evening rush hour, in a street where car auctions are held, a BBC correspondent in the city said.
Iraq 'in crisis'
Mr Mahdi's comments came a day after US Secretary of State Condoleezza Rice and British Foreign Secretary Jack Straw ended a visit to Baghdad to press for swifter movement on establishing a government of national unity.
He told the BBC's HARDtalk TV programme he had urged Mr Jaafari to step down pointing out "that the country is already in crisis and we have to find an end to that".
Mr Jaafari has so far failed to get the approval of minority political groups in parliament in his efforts to form a national unity government, and was also facing rejection within his own United Iraqi Alliance (UIA), Mr Mahdi went on.
"After such a time of naming him, not getting approval of others, now even in the UIA there is some rejection, so I think he should step aside," he said.
But he revealed that Mr Jaafari was determined to press ahead with his nomination, " and he's willing to go to the parliament.... he will welcome the decision of the parliament".
Mr Mahdi lost to Mr Jaafari by one vote in the contest within the Shia alliance for the nomination and is still considered a possible candidate for the prime minister's job.
His comments add significantly to the pressure on Mr Jaafari, the BBC's Mike Wooldridge in Baghdad says.
The US was reported in Baghdad last week to have taken a similar view of Mr Jaafari's position.
The first public calls within Mr Jaafari's own alliance for his withdrawal came at the weekend, but they were from less senior figures.
There are, however, some within the Shia bloc who are concerned that a growing challenge to Mr Jaafari would leave the alliance divided and weak, our correspondent says.
Iraq's political parties have been wrangling over forming a new government since December's election.
Kurdish and Sunni Arab parties rejected the ruling Shia-led bloc's nomination of Mr Jaafari as prime minister and have threatened to boycott a government unless he withdraws.
The delay in forming a government is thought to be partly responsible for fuelling the increasing sectarian violence which has struck since February's bombing of a key Shia shrine in Samarra.