|Protesters in Yemen have been seeking the ouster of President Saleh [EPA]
Yemen's president has for a second time backed out of a Gulf-sponsored deal to transfer power.
The long awaited agreement brokered by the Gulf Co-operation Council (GCC) would have seen Ali Abdullah Saleh stepping down within a month.
Yemen's opposition had earlier said the deal would be signed on Wednesday.
But the head of the GCC, a group of Gulf states, left Sanaa, the capital, without securing a signed agreement.
The departure of Abdullatif al-Zayani suggested that differences remained despite the government and opposition earlier agreeing on the deal in principle.
Zayani had been in Sanaa since Saturday to try to persuade the sides to sign the deal, with help from US and European diplomats.
"Saleh wants to show the international community that he is not an oppressor and a dictator, that he is willing to leave power peacefully and democratically, where in reality that is not the case," Hakim al-Masmari, editor-in-chief of the Yemen Post, told Al Jazeera.
Masmari said Saleh's backtracking on his initial agreement "is only putting him in a bad image and showing the world that his words are not credible and that he has lied not only to the opposition but also to the GCC officials".
Urging political reform
The White House, meanwhile, urged Saleh to sign and implement a transition of power deal so that the country could "move forward immediately" with political reform.
John Brennan, an adviser to Barack Obama, the US president, called Saleh earlier in the day, the White House said in a statement.
"Brennan noted that this transfer of power represents the best path forward for Yemen to become a more secure, unified, and prosperous nation and for the Yemeni people to realize their aspirations for peace and political reform," the statement said.
Brennan also reiterated that all parties in Yemen should "refrain from violence and proceed with the transition in a peaceful and orderly manner".
Earlier, Al Arabiya television had quoted an adviser to Saleh as confirming the signing would take place on Wednesday.
The opposition, whose coalition includes Islamists and leftists, said that among the minor modifications in the deal were changes in who would sign and in what capacity for the opposition and for the government.
"The president will sign for the government in his capacity as president of the republic and as head of the ruling party," Yahya Abu Usbua, an opposition official, told the Reuters news agency earlier.
Modifications proposed by the ruling party, passed on to the opposition by diplomats, would let the ruling party appoint a unity government for the transition period until elections and would also change which opposition representative would sign the deal, the opposition leader said.
But some protest groups had said they would not accept the GCC plan.
Saleh, who has outlasted previous opponents' attempts to challenge his power, indicated in April he would sign the Gulf deal, but refused to put his name to it in the final hours.
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He said at the time he would only sign in his capacity as ruling party leader, not as president.
He and his party had then agreed that he would sign as president of both the party and the country.
The US and neighbouring oil giant Saudi Arabia, both targets of foiled attacks from al-Qaeda's Yemen wing, have been keen to see an end to Yemen's political stalemate out of concern that continued chaos could give the group more room to operate freely.
On Tuesday, Yemenis marked 100 days of protest against the government.
In the southern port city of Aden, gunmen in civilian clothes fired into the air at a protest camp early on Tuesday morning.
Protesters said that this was an apparent attempt to scare them out of the area they have camped out for months, demanding Saleh's immediate ouster.
Residents and medics said several were hurt but no one was killed. Fleeing protesters, some of whom hurled stones at their attackers, quickly returned to their camp after the clashes.
Elsewhere in the south, gunmen shot dead two soldiers and a civil servant as they drove up in a lorry to a security checkpoint in the southern city of Mukalla, a local official said.