The U.N. Security Council on Tuesday called on President Bashar al-Assad to keep a Thursday deadline for a complete ceasefire in the Syria conflict.

In a statement read by U.S. ambassador Susan Rice, the council backed a demand by U.N.-Arab League envoy Kofi Annan for the Syrian government to make a "fundamental change of course" to end hostilities by 6:00 am Damascus time on Thursday.

An explosive device was thrown at a convoy carrying the head of the United Nations mission to Libya on Tuesday, a U.N. spokeswoman said, adding that there were no casualties.

"While on a visit to Benghazi, the head of the United Nations Support Mission to Libya had what appeared to be an explosive device thrown at his convoy," Hua Jiang said.

The Palestinians have sent a letter to the United Nations Security Council seeking condemnation of Israeli settlement activity, the Palestinian foreign minister said on Tuesday.

Riyad al-Malki said the Palestinian envoy to the U.N., Riyad Mansour, had submitted letters to the council and U.N. Secretary Ban Ki-Moon on Monday, ahead of a meeting of the peacemaking Quartet in Washington on Wednesday.

Ninety people including 66 civilians were killed across Syria on Tuesday, the day the government was expected to pull its forces from protest hubs under a U.N.-Arab League peace plan, monitors said.

The Local Coordination Committees, the main activist group spurring protests on the ground, said security forces killed 30 people in Homs, nine in Idlib, 22 in Hama, five in Daraa, two in Aleppo, one in the Damascus suburb of Harasta and one in Deir al-Zour.

Libya, which wants Moammar Gadhafi’s son Seif al-Islam tried at home, on Tuesday appealed a ruling by the Hague-based International Criminal Court (ICC) that he be handed over to the world court.

The ICC, which wants to try Seif on charges of crimes against humanity for his role in battling last year's uprising which toppled his father, issued a ruling on April 4 calling for his immediate transfer from prison in Libya to prison in The Hague.

A Saudi human rights group voiced alarm on Tuesday about the health of one of its members, who has been on hunger strike for almost a month and who stopped drinking water at the weekend.

"The interior ministry... carries full responsibility over the deteriorating health condition of prominent rights activist and member of the association Mohammed bin Saleh al-Bajadi," the Saudi Civil and Political Rights Association (ACPRA) said.

Syrian forces on Tuesday pounded protest hubs in apparent breach of a ceasefire deal brokered by U.N.-Arab League envoy Kofi Annan, who appealed for his plan to be implemented without preconditions.

Syria said it was abiding by the plan, but Annan accused Damascus of pulling troops from some areas and moving them to others, and the rebel Free Syrian Army warned it would resume attacks if the government offensive does not stop.

Iran's intelligence ministry said it has broken an Israeli-linked "terror and sabotage" network which had its headquarters in an unspecified nearby country, media reports said on Tuesday.

"One of the Zionist regime's biggest terror and sabotage networks and some of its agents have been identified. A group of criminal terrorists and mercenaries cooperating with them has been arrested," the ministry said in a statement picked up by the Iranian outlets.

The rebel Free Syrian Army will resume attacks on forces loyal to President Bashar al-Assad if the regime does not stop shelling and pull troops out of protest hubs as promised, its spokesman warned Tuesday.

"If (the regime) does not stop shelling and not withdraw tanks, we will intensify our military operations and launch attacks," Colonel Qassem Saadeddine told Agence France Presse.

The Syrian National Council said on Tuesday that the Damascus regime had so far failed to comply with a U.N.-backed peace plan and described new conditions it set as "unacceptable and unrealistic".

The use of heavy weaponry and mortar shelling has been reported on Tuesday, the day the plan had called for Syrian troops to pull out of rebel cities, SNC spokeswoman Basma Qoudmani said on a visit to Geneva.