The UN envoy to Yemen, Jamal Benomar, called on Monday for a rapid transfer of power in the unrest-swept country, following talks with dissident General Ali Mohsen al-Ahmar.
"The time has come to speed up change in Yemen and begin a power transfer," Benomar told reporters.
"The UN Security Council resolution is a clear message from the international community that time has come for a political agreement," he added.
The UN Security Council had adopted a resolution strongly condemning deadly government attacks on demonstrators in Yemen.
It has backed a Gulf plan under which President Ali Abdullah Saleh would hand power over to his deputy in return for immunity from prosecution for himself and members of his family.
"Transfer of power from President Ali Abdullah Saleh to his deputy Abdrabuh Mansur Hadi is inevitable and is supported by international law," said Ahmar after the meeting.
However, a diplomat in Sanaa told AFP that Benomar's efforts were "overshadowed by pessimism."
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"The Yemeni president seems to insist on remaining a president throughout the transitional period until the new presidential election -- whether this period lasts six months or two years," he said.
Saleh was also "very reserved on the issue of restructuring military and security bodies," led by his relatives, said the diplomat, who spoke to AFP on condition of anonymity.
The longtime president has come under domestic and global pressure to step down in line with a UN roadmap which calls on him to hand over power to Hadi, who would then lead a two-year-long transitional period.
The interim period would see the formation of a reconciliation government, restructuring of military bodies and drafting of a constitution, according to Yassin Saeed Noman, head of the Common Forum that groups parliamentary opposition parties.
The roadmap, drawn up in two weeks in July during talks between Benomar and the opposition and leading figures of the ruling party, provides an implementation mechanism for the Gulf-brokered plan which Saleh has stalled for months.
The diplomat said Western countries were considering sanctions on the president and his son Ahmed, who commands elite Republican Guard units, as well as on the dissident general and Hamid al-Ahmar, leader of the Islamist Al-Islah party.
"These sanctions are aimed at putting more pressure on Yemeni counterparts to give in to a peaceful solution" to the country's political turmoil, he said.
Several hundred people have been killed since protests against the president that erupted in January degenerated into battles between rival troops backed by tribesmen from both sides.