Syria has resumed an aerial attack on the rebel-held town of Ras al-Ain, near the border with Turkey, dropping two bombs on a Syrian security building that had been captured by the rebels, according to an official from the mayor’s office in the Turkish border town of Ceylanpinar.

Turkish ambulances rushed to the border on Monday and at least 11 wounded Syrians were brought to the hospital in Ceylanpinar for treatment.

Shrapnel from the bombing landed on Turkish territory, but no one was injured, officials said.

The official spoke on condition of anonymity in line with Turkish government rules that prevent civil servants from speaking to journalists without prior authorisation.

The attacks came a day after Syrian fighter jets and artillery blasted parts of the capital, Damascus, and its suburbs on Sunday.

Also on Monday Fierce fighting erupted in the Aleppo district of Bustan al-Basha on Monday as troops advanced for the first time into the stronghold of opposition firghters, a military source and resident told AFP.

The Syrian troop advance came on the fourth day of fighting in the northern district, which has been controlled for months by rebels from the opposition battalions of Al-Nusra Front and Ahrar al-Sham.

The resumed bombings also coincided with Russian President Vladimir Putin’s trip to Istanbul.

Russia and China have used their veto power at the UN Security Council to block any sanctions imposed on President Bashar al-Assad’s regime over its crackdown on the uprising that began in March 2011.

The UN also said on Mondaythat it was suspending its aid operations in Syria and withdrawing all non-essential international staff due to the worsening security situation.

Against this backdrop, the Syrian foreign ministry said in a statement on state television on Monday that the government would not use chemical weapons, if it had them, against its own people.

“In response to the statements of the American secretary of state, who warned Syria against using chemical weapons, Syria has stressed repeatedly that it will not use these types of weapons, if they were available, under any circumstances against its people,” the statement said.

Syria’s conflict started 20 months ago as a protest against Assad, whose family has ruled the country for four decades. It quickly morphed into a civil war, with rebels taking up arms to fight back against a crackdown by the government.

According to activists, at least 40,000 people have been killed since March 2011.