Rebel fighters battled regime troops inside the walls of the sprawling central prison compound in Syria's largest city Wednesday, hours after blowing open the gate with twin car bombs in an attempted jailbreak, activists said.

The orchestrated assault began at dawn, but by nightfall, the rebels had not dislodged regime forces or freed some 4,000 prisoners held there, according to two pro-opposition monitoring groups.

Across Syria, the Internet was restored after a blackout of more than eight hours, the second nationwide outage in a week. Syria's Communications Ministry blamed a rebel bombing that it said cut a cable north of Damascus but gave no details.

At the United Nations, the General Assembly voted 107-12 with 59 abstentions to approve an Arab-backed resolution calling for a political transition in Syria and condemning President Bashar Assad's regime for "gross violations" of human rights.

Earlier this month, the U.S. and Russia agreed on a joint push to get Syria's political opposition and representatives of the Assad regime to negotiate a peaceful transition in Syria. An international conference, possibly in early June, would help launch such talks.

However, both the opposition and the regime have said they want to hear more about the agenda, the venue and the participants before signing up. The two sides remain far apart on the terms, with the opposition insisting Assad must step down first and the regime unwilling to commit to an open-ended cease-fire.

British Prime Minister David Cameron called for urgent action to pressure the Syrian government and opposition to put forward names for a transitional government that everyone can support so negotiations can begin.

"My concern is that we'll get into too long a process," he told reporters after meetings at the United Nations.

The Syria conflict began with a popular uprising in March 2011 and escalated into a civil war that has claimed more than 70,000 lives.

On Wednesday, rebels launched an assault on the central prison in the northern city of Aleppo after weeks of fighting in the area, in an attempt to free some 250 regime opponents believed to be held there, according to the Britain-based Syrian Observatory for Human Rights and a local activist group, the Aleppo Media Center.

The attack began with two simultaneous car bombs detonated at the entrance of the prison, the Observatory said.

The Observatory and the Aleppo Media Center said rebel fighters then surged into the compound and seized one of the buildings.

By Wednesday evening, battles continued to rage inside the compound, the Observatory said.

The group said at least 15 regime soldiers were killed, although it did not have the number of rebel casualties.