BEIRUT — Syrian President Bashar Al-Assad's troops battled rebels in the outskirts of Damascus Wednesday and pressed on with a counteroffensive against opposition fighters in the south to prevent their advance on the capital. The fighting came as US Secretary of State John Kerry was meeting with Syrian opposition leaders in London to discuss ways to step up aid to rebels fighting to topple the regime in Damascus. With the recent influx of better weapons and other foreign aid, the rebels have made major gains in the south, seizing military bases and towns in the strategically important region between Damascus and the border with Jordan, about 160 km from the capital. In their campaign to topple Assad, the opposition fighters hope to eventually storm Damascus from the south. The Britain-based Syrian Observatory for Human Rights said Wednesday's clashes were focused on opposition strongholds around the capital, including the suburbs of Daraya and Harasta. Fighting also raged in and around the northern city of Aleppo, Syria's largest city and its main commercial hub, they said. The activists said both sides sustained losses on the two battlefields. Damascus suburbs and Aleppo have been the scene of major urban warfare in Syria's two-year uprising against Assad's rule. At least 28 rebels and 13 soldiers were killed in the fighting around Damascus, while 15 opposition fighters and 28 government troops died in the fighting in Aleppo on Wednesday, the observatory said. The rebels now control large swaths of northern Syria, and last month captured their first provincial capital, the city of Raqqa. The also control whole districts of Aleppo. The government has been hitting the rebel-held areas in the north with airstrikes in recent weeks, reclaiming some of the territory from the rebels, including several villages along the route that links Aleppo with its airport to the city's east. The rebels have been trying to capture the airport for months, in hope of having their own airstrip to receive aid flights. The airfield and much of the area around the airport, including an air base, remain under the regime's control. Al-Nusra pledges allegiance to Qaeda The head of Syria's jihadist Al-Nusra Front pledged allegiance to Al-Qaeda chief Ayman Al-Zawahiri Wednesday, but distanced his group from claims it had merged with Al-Qaeda in Iraq. The announcement is likely to bolster assertions by the Assad regime that it is fighting “terrorists” who want to impose an Islamic state, and could further complicate Western attempts to help rebel forces. “The sons of Al-Nusra Front pledge allegiance to Sheikh Ayman Al-Zawahiri,” Abu Mohammed Al-Jawlani said in the recording. But, he added, “we were not consulted” on an announcement by Al-Qaeda in Iraq chief Abu Bakr Al-Baghdadi on Tuesday of a merger with Al-Nusra Front. “We inform you that neither the Al-Nusra command nor its consultative council, nor its general manager were aware of this announcement. It reached them via the media and if the speech is authentic, we were not consulted,” Jawlani said. He added that the group would not be changing its flag or its “behavior”. “Al-Nusra Front will not change its flag, though we will continue to be proud of the flag of the Islamic State of Iraq, of those who carry it and those who sacrifice themselves and shed their blood for it,” said Jawlani, acknowledging he had fought in Iraq alongside the ISI, Al-Qaeda's Iraqi branch. — Agencies