Syrian troops on Sunday seized the flashpoint northern town of Jisr al-Shughur, state television said, as international outrage mounted at the regime's harsh crackdown on protesters.

Rights activists had earlier reported heavy gunfire and explosions in the town near the Turkish border after troops backed by helicopter gunships and around 200 tanks launched a two-pronged assault early on Sunday.

State television said the army now completely controlled Jisr al-Shughur and that troops were pursuing "armed elements" into the woods and nearby mountains.

Official media also reported the discovery of a mass grave in the town containing the mutilated bodies of 10 security agents whose hands, head and feet had been cut off.

"Armed groups had mutilated the corpses which were removed from the mass grave," the broadcaster said.

It said the army entered the town "after defusing dynamite placed on the bridges and roads by the armed groups".

It added: "two armed men were killed and many more arrested, with machine guns also seized."

Rights activists told AFP by telephone that the army had bombarded Jisr al-Shughur before entering the town, which was largely deserted after thousands of people fled ahead of the expected onslaught.

"The army started at about 7:00 am (0400 GMT) to shell the town intensively with tanks and heavy weaponry before launching an assault from the east and south," one activist said.

"Explosions were heard and helicopter gunships patrolled over the city."

Another activist, citing residents, said explosions had been heard throughout the morning and columns of smoke could be seen rising from the town.

Jisr al-Shughur is in Idlib province, long a hotbed of hostility towards the regime of President Bashar al-Assad.

It has been the focus of military operations for the past week, following what the authorities said was the massacre of 120 policemen by "armed gangs" in the town on Monday.

Activists and residents deny the allegations of a massacre. They say a number of policemen were executed by other security force members when they refused to fire on protesters in the town.

"The way the regime is currently handling the protests is exactly what caused demonstrations to spread in the first place: security forces detaining, torturing and killing citizens," said Syria's local coordination committees.

The committees, who coordinate protests on the ground, issued a statement calling for Assad's departure and for the creation of a transitional political body to govern the country for six months.

"We shall not accept giving an opportunity to leave Syria hostage to such an irresponsible regime," the statement read.

The crackdown in Idlib has seen more than 5,000 people flee across the border into Turkey, according to latest figures given by Turkey's Anatolia news agency.

Among them were Syrian army deserters who gave detailed accounts of the atrocities committed by soldiers who were themselves were under threat of execution if they disobeyed orders.

Tahal al-Lush described an operation in Ar-Rastan, a town of 50,000 people in Homs province, that had pushed him to desert.

"We were told that people were armed there. But when we arrived, we saw that they were ordinary civilians. We were ordered to shoot them," said Lush.

"When we entered the houses, we opened fire on everyone, the young, the old... Women were raped in front of their husbands and children," he said.

Their accounts tally with those gathered by US-based Human Rights Watch, which at the beginning of June released a report alleging systematic killings and torture by the Syrian security forces.

Security forces had been given shoot-to-kill orders by the commanders, said the report, which was based on interviews with more than 50 victims and eyewitnesses.

The latest harrowing accounts have sparked fresh international outrage with the the United Nations, the United States and the European Union all urging Assad to end the violence.

Assad's crackdown on pro-democracy protests that erupted in mid-March has killed more than 1,200 civilians, rights groups say.

Both the EU and the US are backing a UN Security Council resolution proposed by Britain and France that condemns Syria for its crackdown.

"The dangerous situation makes a clear reaction from the UN Security Council all the more urgent," German Foreign Minister Guido Westerwelle, whose country currently holds a non-permanent seat on the council, said in a statement.

But Russia and China, both veto-wielding council members, oppose any such resolution.

Damascus blames the unrest on "armed terrorist gangs" backed by Islamists and foreign agitators.

It is not possible to verify the accounts as foreign journalists are not allowed to circulate freely in Syria.