It remains unclear whether the device might have been planted by someone from the outside who gained access to the mosque, or someone within Saleh’s inner circle.

Saleh initially blamed the June 3 attack on an “outlawed gang” of his tribal foes.

The blast killed seven people, wounded senior officials and forced Saleh’s evacuation to Saudi Arabia for treatment. There have been conflicting reports about his condition — ranging from fairly minor to life-threatening burns.

Yemen’s Embassy in Washington said on Wednesday that Saleh was in stable condition “and continues to improve.”

Yemeni officials have previously described the blast as the result of a rocket attack. But US and Arab officials, all speaking on condition they not be named, said an investigation into the blast suggested it was caused by an explosive device.

With Saleh outside of Yemen, Western and Arab powers are pressing for a negotiated transition of power there, following months of pro-democracy protests that have tipped the impoverished country to the brink of civil war.

Saleh, in power for three decades, had long been viewed as a crucial US ally who allowed US forces to conduct clandestine operations, including unmanned aerial drone strikes, against Al Qaeda’s local offshoot — Al Qaeda in the Arabian Peninsula, or AQAP.

The group claimed responsibility for a failed Christmas Day attack in 2009 aboard a US airliner and an attempt in October 2010 to blow up two U.S.-bound cargo planes with explosive parcels. US officials see AQAP as perhaps the most potent foreign terrorism threat.