Syrian troops backed by members of Lebanon's Hezbollah group began a major offensive Saturday under the cover of intense airstrikes to retake a rebel-held mountain resort while opposition fighters retaliated by shelling the capital Damascus.

Taking the rebel-held town of Zabadani would tighten Hezbollah's grip on Syrian territories bordering Lebanon and would strengthen the Syrian government's control over of the Beirut-Damascus highway.

Zabadani has been held by rebels since shortly after Syria's crisis began in March 2011. The conflict has killed more than 220,000 people and wounded at least a million, according to the United Nations.

The shells fired by rebels into Damascus struck several neighborhoods including the central Baghdad Street district. Another shell hit Damascus' famous Dama Rose hotel, previously Le Meridien, near the posh neighborhood of Abu Rummaneh.

The shelling caused damage to the hotel shattering some of its windows. The Syrian state news agency reported that one person was killed and two others wounded.

Hezbollah's Al-Manar TV aired footage from the battlefield showing smoke billowing from much of Zabadani as shells and missiles struck the town.

Al-Manar said Hezbollah's fighters and Syrian troops are attacking from several directions adding that rebels are now isolated inside Zabadani, which is surrounded by mountains.

Syrian state TV quoted an unnamed military official as saying that "terrorists suffered large losses."

The Britain-based Syrian Observatory for Human Rights said the government's air forces conducted 15 airstrikes on Saturday morning. It said the attack was being conducted by Hezbollah and Syria's elite 4th Division.

Syrian troops and Hezbollah intensely bombarded Zabadani on Friday. The Observatory said the resort was subjected to more than 90 airstrikes on Friday alone.

Saturday's offensive came a day after a bomb exploded inside a mosque where al-Qaida's branch in Syria was holding a fast-breaking meal, killing at least 14, activists said.

The activists said the bombing inside the Salem Mosque in the northwestern town of Ariha occurred shortly after sunset Friday when scores of Nusra Front members gathered to break their fast during the Muslim holy month of Ramadan.

The Observatory reported Saturday that the explosion killed 31 Nusra Front members including five commanders.

Syria-based activist Ahmad al-Ahmad said 15 Nusra Front fighters were killed and more than 30 wounded. He said the Nusra Front commander in Idlib province, Abu Abdullah al-Tunisi, was either wounded or killed in the blast.

The differences in casualty estimates could not be immediately explained since the Nusra Front cordoned off the area.

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No one claimed responsibility for the attack although activists said President Bashar Assad's government might have been behind it.

Ariha was a government stronghold until it was captured by the Nusra Front and its allies in May.