The United States and its allies are pushing Saleh to hand over power to his deputy under a Gulf proposal aimed at ending unrest that has pushed Yemen close to a civil war.

"We believe he was seriously injured ... He is not coming (home) in the coming days, he is not coming (home) soon," the diplomat told Reuters.

The United States has been helping Yemen investigate the attack, which killed several people and also wounded the prime minister, two deputy prime ministers and the speakers of both parliamentary chambers.

The diplomat said an initial investigation showed Saleh was injured in the explosion from a TNT charge planted inside a mosque within the presidential palace in Sanaa on June 3.

A source close to the investigation, asked about the number of charges planted at the mosque, said: "Six explosives were planted inside the mosque. Only one went off."

Yemeni officials earlier accused an opposition tribal coalition of shelling the palace, a charge they denied.

The Arab country has been rocked by months of protests demanding an end to Saleh's 33 year-rule, which has driven Yemen close to financial ruin.

The proposal by Gulf neighbors calls for Saleh to hand power over to his deputy, Vice President Abd-Rabbu Mansour Hadi, who is acting president, as a step toward forming a new government and preparing for elections.

Jeffrey Feltman, the US Assistant Secretary for Near Eastern Affairs, met Hadi and other senior Yemeni officials in Sanaa on Wednesday. "It is time for Yemeni political leaders to work together for an immediate and peaceful transition of power," Feltman told a news conference in Sanaa on Thursday.

Asked if there was pressure on Saleh not to go back to Yemen, Feltman said: "We expect the president to take a decision in the best interests of the Yemeni people. It is a Yemeni decision, not an American decision."