BEIRUT: Syrian warplanes carried out airstrikes on rebels trying to storm a police academy outside Aleppo on Wednesday, activists said, while jihadi fighters battled government troops along a key supply road leading to the southeastern part of the city, activists said.

The latest fighting came as the new U.S. secretary of state said Washington is looking for more concrete ways to help the rebels in their fight to oust President Bashar Assad.

Aleppo, Syria's largest city and former commercial capital, became a key front in the country's civil war after rebels launched an offensive there in July 2012. In months of bloody street fighting, opposition fighters have slowly expanded the turf under their control, although the combat has left much of the city in ruins.

The police academy has recently emerged as a new front in the fight for the city, which is considered a major prize in the conflict.

Activists say the government has turned the facility into a military base, using it to shell opposition areas in the countryside as well as rebel-held neighborhoods inside the city.

The Britain-based Syrian Observatory for Human Rights said clashes raged Wednesday around the complex.

"The rebels are still trying to storm the school, but they can't because the regime is carrying out airstrikes and bombarding rebel forces," Observatory director Rami Abdul-Rahman said.

He said at least six rebels were killed Wednesday, bringing the three-day death toll to 37 opposition fighters and more than 50 regime troops.

Another key front in the battle for control of Aleppo is the city's international airport. Rebels have been trying for months to seize the facility, and have made headway in recent weeks, overrunning checkpoints and capturing a military base charged with protecting the airport.

The government is desperate to hold onto the airport, which it has used in the past to fly in supplies to its troops bogged down in the city. However, the fighting has forced the government to close the airport to flights and try to send supplies and reinforcements overland.

Most of those reinforcements, including dozens of vehicles and thousands of troops, are now stuck in the city of Safira, southeast of Aleppo, according to Abdul-Rahman. Fighters from Jabhat al-Nusra, an Islamic extremist rebel group that the U.S. has designated a terrorist organization, have cut the road leading from Safira to the airport, and for weeks have battled troops along the road, preventing them from pushing north to the city to link up with government troops there.

The Observatory reported fierce clashes north of Safira on Wednesday, with both sides shelling each other with mortars and artillery.

The rebels have notched a number of strategic victories in recent weeks that appear to mark a shift in momentum in the nearly 2-year-old conflict, which the U.N. says has killed some 70,000 people. Already in control of much of the countryside in the northeast, the rebels have captured the nation's largest hydroelectric dam, a major oil field and two army bases.

They have also been peppering the center of Damascus with mortar shells as part of their effort to bring the fighting from the capital's rebel-held suburbs into the center of the city. On Wednesday, the Observatory said several mortar shells exploded near the military judiciary and the literature department of Damascus University.

Part of the rebel strategy appears to be to try to shatter the sense of normal life that Assad's regime has desperately tried to maintain in the capital, which has been insulated from much of the violence ravaging the rest of the country.

In Paris, U.S. Secretary of State John Kerry said Washington is looking for more tangible ways to support Syria's rebels and bolster the Western-backed political opposition that would "accelerate the political transition that the Syrian people want and deserve."

So far, the U.S. has largely limited its assistance to funding for communications and other logistical equipment. A decision on whether to vastly increase the size and scope of aid - including pre-packaged meals and medical supplies - is expected by Thursday when Kerry will attend an international conference on Syria in Rome, officials in the U.S. and Europe said.

The Obama administration has not sent military equipment to the rebels, in part out of fears it could fall into the hands of Islamic militants who could use it for terrorist attacks.

The officials spoke on condition of anonymity because the shift in strategy has not yet been finalized and still needs to be coordinated with European nations.

The civil war has forced hundreds of thousands of Syrians to flee their homes and seek shelter elsewhere inside the country or abroad.

Anmar Hmoud, a government spokesman for Syrian refugee affairs, said Wednesday new surge has seen around 3,000 refugees a day escaping across the border into the kingdom as fighting intensifies in southern Syria. The influx has pushed the total number in Jordan to nearly 420,000.

The U.N. says there are nearly 925,000 displaced Syrians scattered throughout the region.

Syria's state news agency said the Interior Ministry on Wednesday extended the validity of passports from six to 10 years, starting from January 2013. Syrians outside the country holding expired passports will be able to renew their documents for two years, SANA said.

The move appeared to meet a demand of Syria's exiled opposition leaders, who have pressed the government to renew passports of the hundreds of thousands of Syrians who have sought refuge abroad and now find their papers no longer valid, potentially trapping them outside the country.

The opposition is certain to monitor whether the order is indeed implemented at the embassy level, or whether it remains on paper only.