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At least 30 people have been killed by a suicide truck bombing on the edge of the central Syrian city of Hama.
State news agency Sana said Syrian rebels had driven a truck laden with over a tonne of explosives into a government checkpoint on a busy road.
The explosion appears to have set ablaze a nearby petrol tanker, increasing the damage and casualties.
The UK-based Syrian Observatory for Human Rights said the al-Qaeda-linked al-Nusra Front carried out the attack.
"A man detonated a truck laden with explosives at a checkpoint near an agricultural vehicles company on the road linking Hama to Salamiya," the Observatory said.
It said the attack had targeted government soldiers, but that most of the dead were civilians.
Pictures on Syria TV showed firemen battling to contain fires as black smoke rose from charred trucks and cars.
A man who received leg injuries in the blast told Syrian state TV: "I was heading to a school in Salamiya and the blast started.
"These innocent people don't deserve this. The scene is inhumane. These terrorists shouldn't be in this country."
Hama saw some of the largest demonstrations against the rule of President Bashar al-Assad in the first months after the Syrian uprising began in March 2011.
But in late summer 2011, security forces stormed the city and have maintained control ever since.
Hama occupies a significant place in the history of modern Syria. In 1982, then-President Hafez al-Assad, father of Bashar, sent in troops to quell an uprising by the Sunni opposition Muslim Brotherhood. Tens of thousands were killed and the town flattened.
Meanwhile, the head of the Arab League has said that a long-awaited conference on Syria will begin on 23 November, although this falls short of a formal announcement.
Nabil el-Arabi was speaking after meeting the international envoy on Syria, Lakhdar Brahimi, who is on a tour of the Middle East to prepare for the conference.
Mr Brahimi did not himself publicly set a date, saying he would do so after his tour. Mr el-Arabi conceded that there were still many obstacles ahead.
Western and Arab government officials will meet Syrian opposition leaders on Tuesday to try to persuade them to attend.