Fighting raged on Saturday in the Yemeni capital, leaving at least 40 dead as forces loyal to President Ali Abdullah Saleh battled pro-opposition soldiers and moved to clear the protest camp at a Sanaa square that has been the epicentre of the country’s uprising.

The latest spasm of violence came a day after Mr. Saleh suddenly returned to Yemen after more than three months of being treated in Saudi Arabia following an assassination attempt on him in June. Mr. Saleh’s return on Friday apparently aimed to ensure his grip on power as his loyalists and opponents wage urban warfare in Sanaa.

Mr. Saleh’s forces were battling on three fronts on Saturday.

In the northwest section of Sanaa, mortars rained down on the headquarters of the 1st Armoured Division, led by Mr. Saleh’s former ally Maj. Gen. Ali Mohsen al-Ahmar who months ago sided with the opposition and whose followers have since been protecting the protesters’ daily sit-ins and marches on Change Square.

Eleven of Maj. Gen. al-Ahmar’s troops were killed in the shelling and 112 were wounded, according to Abdel-Ghani al-Shimiri, a spokesman for the turncoat soldiers.

Around the square itself, Republican Guard forces led by Mr. Saleh’s son, Ahmed, along with Central Security forces battled Maj. Gen. al-Ahmar’s troops in an attempt to clear the square of protesters and end more than seven months of their encampment that has demanded Mr. Saleh’s ouster.

Using anti-aircraft guns, automatic weapons and RPGs, Guard forces intensified the shelling of the streets surrounding the square, while large number of snipers on rooftops hunted down protesters.

Mohammed al-Qabati, a medic who works at the field hospital set up at the square, said 29 people were killed there since the early hours on Saturday, both from among the protesters and the troops guarding them.

He said 54 people were also wounded in the attack.

“More bodies and injured are pouring into the hospital,” said Dr. al-Qabati, adding that ambulances have been forces to leave many bodies in the streets because of the heavy fighting. “Many of the injured get here by motorcycles.”

The scene was chaotic as thousands of protesters ran back and forth searching for a cover in nearby buildings, and witnesses said several houses were wrecked when hit by mortars as street battles raged between rival groups of soldiers.

Meanwhile, Yemen’s Interior Minister, Gen. Mouthar al-Masri, told reporters on Saturday that eight government troops were killed and dozens of others were wounded. Gen. al-Masri didn’t elaborate when or how the casualties occurred, and it wasn’t clear if he was referring to violence in Sanaa or elsewhere.

The third front by Mr. Saleh’s troops centred around Sanaa’s district of Hassaba. Clashes there over the past two days between government forces and pro-opposition tribesmen killed 18 tribal fighters, according to a statement on Saturday from tribal elders.

Hassaba is home to Yemen’s most powerful tribal confederation, the Hashid, led by Sheik Sadeq al-Ahmar, another foe of Mr. Saleh’s. The two Ahmars are not related.

Saturday’s bloodshed also reinforced fears that Mr. Saleh’s presence in the country has escalated the fighting into a full-fledged attempt to crush his rivals.

His return had caught the White House off guard. U.S. officials conceded it was a surprise and said that Secretary of State Hillary Rodham Clinton wasn’t warned of Mr. Saleh’s plans when she met on Tuesday in New York with the Foreign Minister of Saudi Arabia, which has been working with Washington and Yemen to try to arrange a transfer of power.

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