Four explosions shook the center of the Libyan capital Tuesday, sending plumes of smoke billowing across an area in which strongman Moammar Gadhafi has his residence, an Agence France Presse correspondent witnessed.

The first blast rocked Tripoli at 10:45 am (0845 GMT) and was followed by three others.

Vandals tried to set fire to a mosque in the northern West Bank, causing damage to the inside, Palestinian security sources said on Tuesday, blaming Jewish settlers.

The attackers set fire to a number of tires inside the mosque in al-Mughayyir village, some 20 kilometers northeast of Ramallah, which damaged prayer mats inside the building.

Heavy clashes between troops and suspected al-Qaida gunmen at the gates of the southern Yemen city of Zinjibar left 15 people dead, nine of them soldiers, the military and medics said Tuesday.

The fighting erupted overnight when troops advanced on Zinjibar, capital of Abyan province, as they prepared to wrest it back from the control of suspected al-Qaida militants, who overran most of it on May 29.

U.S. Secretary of State Hillary Clinton gave a cool welcome Monday to a French plan to host a Middle East peace conference, saying it must be linked to a willingness to resume talks.

"The idea of any gathering, conference or meeting has to be linked to willingness by the parties to resume negotiating," the chief U.S. diplomat said during a press conference with her French counterpart Alain Juppe.

The White House called Monday for an "immediate transition" of power in Yemen, where the United States fears al-Qaida could exploit political turmoil and strengthen its presence.

After four months of deadly unrest, Ali Abdullah Saleh's 33-year-old regime was teetering even before the president was wounded in an attack on his palace and flown late Saturday to neighboring Saudi Arabia for treatment.

Some 120 Syrian police officers taking part in security operations alongside the army in the northwest were killed by "armed gangs" in the town of Jisr Shugour on Monday, state-run news agency SANA quoted a Syrian official as saying.

"The armed groups are committing a veritable massacre. They have mutilated bodies and thrown others into the Assi river," state television reported earlier. "They have burned government buildings."

Protesters demanded a swift transfer of power from Ali Abdullah Saleh as his deputy said the veteran Yemeni president would return within days after surgery in Riyadh for blast injuries.

EU foreign policy Chief Catherine Ashton on Monday urged Saleh to act "in the best interest of his people" while the White House called for an "immediate transition."

The Muslim Brotherhood's political party, set up to run in polls, was declared legal in Egypt on Monday, state news agency MENA said, for the first time since the movement was founded eight decades ago.

"The commission on party affairs has given its approval for the formation of the Freedom and Justice Party," it said.

NATO air raids targeted the communications of Moammar Gadhafi's battered regime in Libya on Monday, hitting offices of the state broadcaster and his military intelligence headquarters, officials said.

The air strikes came ahead of a visit to Libya by an envoy from Russia, which has raised concerns about the scope of the military campaign.

Israeli Defense Minister Ehud Barak said on Monday that Syrian President Bashar Assad may be encouraging unrest on the Israel-Syria frontier in a futile effort to save his regime.

"We have no choice, we have to defend our border and Assad, in my opinion will fall in the end," said Barak a day after hundreds of protesters from Syria tried to cross into the Israeli-controlled Golan Heights.