Syrian troops battled rebels near Damascus on Saturday and launched air strikes on opposition strongholds in the south of the capital and on its northeastern outskirts, a watchdog said.

The Syrian Observatory for Human Rights gave an initial toll of 49 people killed nationwide, including 16 civilians and 16 rebels killed in Damascus province alone.

To the northeast of the capital, seven civilians including a child were killed in heavy army shelling on the town of Misraba. Nearby, warplanes bombarded the town of Douma and areas between Harasta and Irbin, said the watchdog, adding that 10 rebels were killed in fierce clashes with troops in the area.

The Observatory also reported three rebels and two civilians killed in shelling on southern areas of the capital, including in Daraya, where troops had launched a major military operation to try and seize control of the town.

Syria warned on Saturday that rebels could use chemical weapons in their fight against President Bashar al-Assad’s forces, and insisted that the regime will never unleash such arms on its own people.

British Foreign Secretary William Hague, however, said there was evidence the Damascus government could actually employ chemical weapons stocks in the conflict which a rights group says has killed at least 42,000 people in nearly 21 months.

“Terrorist groups may resort to using chemical weapons against the Syrian people... after having gained control of a toxic chlorine factory” east of Aleppo, the foreign ministry said, using the government term for rebel groups.

It added that Damascus would never use such weapons against its own people.

The ministry was believed to be referring to the Syrian-Saudi Chemicals Company (SYSACCO) factory near Safira, which was taken over earlier this week by militants from the jihadist Al-Nusra Front.

Syria “is defending its people against terrorism, which is supported by known countries, with the United States at the forefront,” the ministry said.

Global concerns over Syria’s chemical weapons stockpiles grew after US officials this week privately said the regime had begun mixing precursor chemicals that could be used for the lethal nerve agent sarin.

Some media reports said that the substance had been loaded into bombs for warplanes. Hague said on Saturday there was evidence Syrian government forces could use chemical weapons against the insurgency. “We are extremely concerned about the stockpiles of chemical and biological weapons, and we are also concerned about evidence during the last couple of weeks that the regime could use them,” he told reporters in Manama on the sidelines of a security conference.

He cited several “dangerous scenarios,” including their “use by the regime” or falling into the hands “of other people.”

Washington has said the use of chemical weapons would be a red line but that it fears rebel battlefield advances could prompt the regime to use them, or that stocks could fall into the hands of groups hostile to the US and its allies.

UN chief Ban Ki-moon said on Friday said it would be an “outrageous crime” if the regime used chemical weapons against the revolt.

The Organisation for the Prohibition of Chemical Weapons, the global chemical weapons watchdog, asked Damascus to sign up to a convention banning their use, citing “serious concerns” that for the first time in the agreement’s history they might be used.

The opposition Syrian National Council said even neighbouring countries would not be spared if such weapons were used.

Syria’s new opposition coalition, meanwhile, said it will announce the creation of a military council before a Friends of Syria meeting next week, to unify insurgent ranks. In mid-November, opposition factions agreed to establish the National Coalition and bring together rebel forces under a supreme military council.

On the ground, the Syrian Observatory for Human Rights reported at least four fighters killed as troops battling rebels near Damascus bombarded opposition strongholds in the south of the city and on its northeastern outskirts.

State television reported that the army had “destroyed a number of vehicles and motorcycles used by terrorists” in Harasta and Daraya. The Observatory said that the army mounted attacks on rebel positions near the borders with Turkey and Israel.

Air strikes struck the northern town of Tal Abyad near Turkey, the Britain-based watchdog said, while shells fell on the villages of Bir Ajam and Al-Buraykah in the Syrian side of the Israeli-occupied Golan Heights.

In the northwestern province of Idlib, four men were killed in air strikes on the village of Kfar Lateh, and warplanes also bombed Maaret al-Numan and the nearby village of Has, killing two men and leaving 15 others wounded. In Aleppo province in the north, warplanes pounded the towns of Aazaz and Jarablus, and targeted rebel positions around the Meng military airport which is ringed by several battalions.