Mr. Saleh has left Yemen to seek medical treatment in Saudi Arabia, and it is understood he is to be operated on soon.

Wounded Yemeni President Ali Abdullah Saleh arrived late Saturday in the capital of Saudi Arabia to receive treatment,the country's ruling party confirmed on Sunday.

"President Saleh arrived in Riyadh along with a number of high-ranking government officials, who were wounded after a shell hit a mosque inside the presidential palace in south of the capital Sanaa," the ruling General Peoples' Congress party's online website said.

The portal did not elaborate further, but also confirmed that Vice President Abdu Rabu Mansour Hadi was assigned to run state affairs in the absence of Saleh, who was hurt in a rocket attack on his presidential palace by tribal gunmen on Friday.

Local media reported that Saleh's family members accompanied him to Riyadh onboard a medical plane which was sent by the Saudi government.

Doctors in Sanaa said Saleh, who has been facing four-month-long mass protest calling for his immediate departure after 33 years in power, was seriously wounded, and one of the injuries was in his chest, 6.7cm from the heart, as his face and chest suffered second degree burns.

According to official sources, Friday's attack left 11 of Saleh's bodyguards dead and a number of high-ranking officials wounded, who were airlifted to Saudi Arabia to get treatment before Saleh's departure.

The attack came after two-weeks of pitched street battles government troopss and armed tribesmen loyal to opposition leader Sadiq al-Ahmar.

A compound belongs to brother of al-Ahmar was heavily attacked minutes after the Yemeni government declared that the presidential palace was attacked by a rocket fired from al-Ahmar's compound in Hadda district.

But media reports said that preliminary investigations suggested that the kind of shell that hit the presidential palace was an advanced type unlike the ones usually used by the tribal militia.