SANA'A: A deal on a transition of power in Yemen fell through at the last minute Wednesday, even as Washington stepped up pressure on President Ali Abdullah Saleh to sign a Gulf-brokered agreement to ease him out of office. Heavy diplomatic wrangling by Western and Gulf diplomats keen to resolve the three-month standoff had secured an agreement in principle that would see Saleh, a shrewd political survivor, resign within a month, an opposition official said. But in a familiar twist, last-minute snags over details derailed the deal that would have granted Saleh immunity from prosecution, allowing him a dignified exit from power in the Arabian Peninsula state he has ruled for nearly 33 years. A government official told Reuters a deal remained possible. “There is still a glimmer of hope,” he said. But the leader of a bloc of Yemen's wealthy oil-exporting Gulf neighbors who has been trying to breathe life into the deal left Sana'a without securing an agreement, in a move that suggests the sides remained significantly at odds. The United States and oil king Saudi Arabia, both targets of foiled attacks from Al-Qaeda's Yemen-based wing, are keen to see an end to the political stalemate, fearing continued chaos could give the militant group more room to operate freely. The White House urged Saleh to sign and implement a transition deal so Yemen could “move forward immediately” with political reform. It said John Brennan, an adviser to President Barack Obama, called Saleh earlier in the day. “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. The opposition, including Islamists and leftists, said the deal tentatively agreed Wednesday contained minor changes to the April deal, on who would sign and in what capacity.“The president will sign for the government in his capacity as president of the republic and as head of the ruling party,” opposition official Yahya Abu Usbua had said. The deal broke down after a dispute on who would sign for the opposition. Saleh wanted the rotating head of the coalition, Yassin Noman, a leftist, to sign. The opposition preferred Mohammed Basindwa, tipped as a possible interim prime minister, sources close to the talks said. The opposition agreed to have Noman as the first opposition signatory, but also wanted Basindwa to be on a list of signatories. Saleh refused and the deal fell through, the sources said. The GCC nations behind the mediation effort were Bahrain, Kuwait, Oman, Saudi Arabia and the United Arab Emirates.