At least 36 people were killed, including 11 defected soldiers, and more than 100 others were wounded when troops loyal to President Ali Abdullah Saleh shelled a camp of protesters and a base of a defected military unit in Yemen's capital Saturday, medics and defected officials said.

"Over than 200 mortar shells, rocket-propelled grenades (RPG) and Katyusha rockets hit the protesters' Change Square, the military base of defected First Armored Division and residential houses," an official of the defected army told Xinhua.

"As many as 11 dissident soldiers were killed and dozens of others were wounded," he said on condition of anonymity.

Medics at the square's field hospital said 25 protesters have been killed since early morning and more than 80 were injured in the continuing attacks on the sit-in camp.

Residents in areas surrounding the square and the defected military base told Xinhua that some 15 residential houses were hit by random shells and nearly 10 civilians were wounded by shrapnel.

The clashes came a few hours after the overnight street battles in the northern edge of Sanaa between government forces and armed tribesmen loyal to Sadiqal-Ahmar, a key opposition tribal leader of Yemeni President Ali Abdullah Saleh.

The fighting flared up hours after Saleh's surprise return to Sanaa early Friday, leaving at least 18 of al-Ahmar's followers dead Friday.

The embattled president, who has confronted eight months of mass protest movement, spent more than three months in the Saudi capital to treat burn wounds he sustained in an attack on his presidential palace in Sanaa on June 3.

In a speech given hours after his arrival, Saleh called for a ceasefire between his troops and the defected army. Earlier Saturday, he ordered a committee formed last week by his deputy Abd-Rabbu Mansour Hadi to lift military checkpoints and end the presence of his troops as well as the defected army, the Defense Ministry said on its website.

Despite Saleh's continuing efforts, deadly battles continued.

An official close to Saleh's office told Xinhua on condition of anonymity that "The clashes will continue till protesters stop shouting their slogans."

The defected army issued a statement Saturday, accusing Saleh of returning to Sanaa "to explode the situation militarily," and warning that "such action will affect the whole Arab region."