Syrian rebels lobbed mortar rounds into central Damascus yesterday, killing at least two people and drawing a fierce army response as bombardments shook the heart of the capital.

The state news agency said mortar bombs fired by “terrorists” had killed two people and wounded others near the Opera House on Ummayad Square, where Baath Party headquarters, Air Force Intelligence and state TV are also located.

The military retaliated with artillery fire from Mount Qasioun, overlooking the city. “I’ve heard dozens of regime shells so far, pounding rebels,” one resident said.

Photos posted by opposition activists showed black smoke rising from the square during what residents said was one of the heaviest bombardments in central Damascus since a revolt against President Bashar al-Assad erupted two years ago.

“The city is under attack,” said one bewildered resident, adding that the explosions had begun at 6.30am.

The conflict in Syria has killed 70,000 people and forced a million to flee the country, the UN says.

Sustained fighting in Damascus could send thousands more into neighbouring states, especially Lebanon, which already hosts 370,000 of them.

There were no immediate reports that the rebels, who have pushed into the Kfar Souseh district, a few hundred metres from Ummayad Square, were trying to advance further.

Assad’s forces have retained control of central Damascus and most other Syrian cities, while losing swathes of territory to insurgents elsewhere, especially in the north and east.

Colonel Riad al-Asaad, founder of the rebel Free Syrian Army (FSA), lost a leg in an overnight blast caused by a bomb placed beneath his car in the opposition-held eastern town of al-Mayadin, his deputy said. A Turkish official said Asaad was now being treated in Turkey and that his life was not in danger.

Asaad, who formed the FSA in 2011 as a popular uprising against Assad turned into an armed rebellion, was one of the first senior officers to defect from the Syrian military, but was sidelined last year from a new Western-backed FSA command.

Asaad’s deputy, Malik al-Kurdi, told Al Jazeera TV he believed the Syrian Government had tried to assassinate the FSA founder with a bomb planted directly below his car seat. He said Asaad had also suffered face wounds.

No group has claimed responsibility for the attack.

Video footage posted online by activists showed Asaad lying on a bed with a bandage on his head and groaning. He was covered in a blue sheet and a man in the film said he would survive. Reuters could not independently verify the video.

Various rebel units fight under the banner of the FSA, which has struggled to find weapons supplies and build a disciplined command and control structure. It does not include some Islamist militants such as the powerful al-Qaeda-linked Nusra Front.

Moaz Alkhatib, who resigned on Sunday as head of the opposition Syrian National Coalition, said the attack on Asaad was part of a drive to “assassinate the free leaders of Syria”.

Despite stepping down, Alkhatib said he would address an Arab League summit in Qatar this week.

“I have decided to give a speech in the name of the Syrian people at the Doha conference,” he wrote on his Twitter account yesterday.

Alkhatib, named leader of the coalition formed in November, is a Sunni Muslim cleric who had been seen as a moderate bulwark against the influence of al-Qaeda-linked jihadist forces.

He resigned after the coalition berated him for offering Assad a negotiated deal and after the group went ahead, despite his objections, with steps to form a provisional government that would have diminished his authority.

The coalition is backed by Western powers and many Arab states, but Russia and China are critical of its insistence that Assad quit as a precondition for negotiations.

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