Yemen President Saleh suffered burns on 40 percent of his body: reports

An attack on Yemeni President Ali Abdullah Saleh's compound Friday severely injured the defiant leader, leaving him with burns on 40 percent of his body and a collapsed lung, U.S. officials told CNN.

Saleh is receiving treatment in Saudi Arabia after the attack at a mosque in his compound. It is unclear if he will return to his country.

An investigation into the Friday assault is ongoing, and Western diplomats told CNN there was possibly a bomb in the compound. A Yemeni official said two projectiles were fired into the mosque.

Protesters in Yemen have been demanding that Saleh step down since January when they took inspiration from other protests in the region. Over the past few weeks, the protests have turned deadly as government forces and tribals have clashed.

Saleh had repeatedly promised to step down, but then refused to sign deals making such a move definite.

The government killed as many as 50 demonstrators in Taiz last week.

Anti-government protesters cheered Saleh's departure to Saudi Arabia and many hoped he would not come back.

Meanwhile, the United States and Saudi Arabia have been working to arrange a power transfer as Saleh receives treatment and is out of the country, the Associated Press reports.

"We are calling for a peaceful and orderly transition, a nonviolent transition that is consistent with Yemen’s own constitution," U.S. Secretary of State Hillary Rodham Clinton said. "We think an immediate transition is in the best interests of the Yemeni people."

Yet a top Yemeni official said Saleh would return home within days.

"Saleh’s health is improving greatly and he will return to the country in the coming days," Vice President Abed Rabbo Mansour Hadi said Monday, AP reports.