BEIRUT - Syrian rebels attacked the main prison in the northern city of Aleppo Wednesday with a pair of car bombs in an attempt to free hundreds of regime opponents believed to be held in the facility, activists said.
Meanwhile, the Internet went down across Syria on Wednesday - the second time in a week - but was restored after more than eight hours.
Aleppo emerged as one of the major fronts in the country's civil war after a rebel offensive there in July, and the fighting since then has settled into a bloody stalemate.
The city, Syria's largest, holds strategic and symbolic value, and both sides have taken significant losses in the battle to expand the turf under their control.
Rebels detonated two car bombs simultaneously outside the walls of the central prison Wednesday morning before trying to storm the facility, according to the Britain-based Syrian Observatory for Human Rights.
That prompted fierce clashes between President Bashar Assad's troops and opposition fighters around the detention center, with at least 15 soldiers killed, Observatory director Rami Abdul-Rahman said. He had no immediate information on casualties among rebels.
The city's central prison is believed to be holding some 4,000 inmates, including 250 jailed for reasons related to the 26-month-old uprising against Assad's regime, said Abdul-Rahman, who relies on reports informants based in Syria.
The fighting continued for hours, but the rebels were unable to reach the area where prisoners are held, according to Abdul-Rahman and the Aleppo Media Center, an activist group in the city.
The Syrian state news agency SANA said regime forces repelled the opposition fighters.
For weeks, rebel fighters have been battling government troops in the area around the prison to try to seize the facility and free the prisoners. Earlier this month, the rebels overran the headquarters of the government's anti-terrorism forces that is located near the jail.
Wednesday's Internet outage began at around 10 a.m. and service was restored more than eight hours later.
Syria's Communications Ministry blamed the outage on rebels, saying a bombing by rebels north of Damascus cut a cable. The ministry did not provide details.
On its Twitter account, SANA had earlier in the day cited a technical problem for the outage.
James Cowie, the chief technology officer of the U.S.-based Renesys Corp. said the cause was not clear.
"It's entirely consistent with a technical fault at a central facility; it's also completely consistent with a decision to use an Internet kill switch," he said in a telephone interview.
Syrian authorities have shut off phone and Internet service in select areas in the past to disrupt rebel communications when regime forces were conducting major operations, although such widespread blackouts have been rare.
Also Wednesday, at least 23 rebel factions, including Islamic extremist groups, joined forces in a push to reopen an arms supply route and retake a key town near Damascus that fell back to regime troops last month.
The rebel groups, including the al-Qaida-affiliated Jabhat al-Nusra, battled government troops around the town of Otaybah, east of the capital, the Observatory said. The army regained control of Otaybah in late April, cutting the opposition's arms route between Jordan and the capital.
There are scores of rebel brigades in Syria. They operate without a unified command structure, but sometimes coordinate to increase their fighting power on individual operations.
In the Yarmouk Palestinian refugee camp in Damascus, clashes erupted after gunmen disrupted a street march to mark the 65th anniversary of Palestinians' mass displacement during the war that followed Israel's founding in 1948, the state news agency said.
While many Palestinians in Syria have remained on the sidelines during the civil war, the Yarmouk camp has been the scene of heavy clashes between a small, pro-Assad group, The Popular Front for Liberation of Palestine-General Command, and armed Palestinians fighting on the opposition side.
More than 70,000 people have been killed since the revolt against Assad's rule erupted in March 2011, and more than a million more have sought shelter in neighboring countries. Millions of others have been displaced inside Syria.
In Jordan, the U.N. refugee agency warned that the relentless fighting has been driving unprecedented numbers of Syrians into neighboring Lebanon, Jordan, Turkey and Iraqis, straining the countries' water and food resources to the limit.
Andrew Harper, the UNHCR representative to Jordan, said the U.N. has received only half of the $1.5 billion pledged by international donors to cover the refugees' needs until June.
A Jordanian government spokesman for Syrian refugee affairs, Anmar Hmoud, said Wednesday that the kingdom hosts 535,000 Syrian refugees, while more 150,000 have found shelter in the Zaatari camp near the border with Syria.
UNHCR expects that total number of Syrians in Jordan could double by the end of the year.
Associated Press writers Raphael Satter in London, Albert Aji in Damascus and Dale Gavlak in Amman, Jordan contributed to this report.