DAMASCUS (AFP) - Syrian troops on Sunday fought violent battles with "armed gangs" in flashpoint Jisr al-Shughur town, state television said, as international outrage mounted at the regime's harsh crackdown on protesters. Syria's official media also reported that a mass grave was found in Jisr al-Shughur, allegedly containing the bodies of security agents killed by the gangs. Rights activists reported heavy gunfire and explosions in the northwestern town near the Turkish border after troops backed by helicopter gunships and around 200 tanks launched a two-pronged assault early on Sunday. "Army divisions entered Jisr al-Shughur and purged the state hospital of armed groups," the television said. "Violent clashes pitched the army divisions against armed groups positioned inside and around the town," it added. The army entered the town "after defusing dynamite placed on the bridges and roads by the armed groups," the report said, adding that "two armed men were killed and many more arrested, with machine guns also seized." A mass grave was discovered in Jisr al-Shughur containing the bodies of security agents from the city's police headquarters, the television later said, without specifying the number of bodies. "Armed groups had mutilated the corpses which were removed from the mass grave," it added. The rights activists, reached by telephone, told AFP the army fired barrages of shells into Jisr al-Shughur before entering the town, largely deserted after thousands fled ahead of the crackdown. "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 that explosions had been heard throughout the morning and columns of smoke could be seen rising from the town. Syria's Idlib province, in which Jisr al-Shughur falls, has long been 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. Human rights activists and residents deny the allegations of a massacre and say a number of policemen were executed by other security force members when they refused to fire on protesters in Jisr al-Shughur. The crackdown in Idlib has seen more than 5,000 people flee across the border into Turkey, according to latest figures given on Sunday by Turkey's Anatolia news agency. As the death toll mounted, detailed accounts emerged from some of the thousands who fled to Turkey from the bloodshed in Idlib. Among them were Syrian army deserters who told of atrocities committed by soldiers in suppressing protests, who themselves were under threat of execution if they disobeyed orders. Tahal al-Lush described the 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, with a blank stare in his eyes. "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. The harrowing reports of atrocities committed during Syria's crackdown have sparked fresh international outrage. UN chief Ban Ki-moon expressed concern at the mounting death toll, while the United States and the EU urged Assad to let aid workers in to help relieve the humanitarian crisis. Washington on Saturday called on Syria to let medics in, after reports that Syrian forces backed by helicopters had the previous day killed at least 25 protesters across the country, including in and around Jisr al-Shughur. Fridays have become a rallying point in the revolt against Assad's regime, whose backlash on pro-democracy protests that erupted in mid-March has killed more than 1,200 civilians, rights groups say. The European Union also appealed to Assad to let international aid agencies in to help civilians caught up in the violence. Both the EU and the US are backing a UN Security Council resolution proposed by Britain and France that condemns Syria for its crackdown. Germany said on Sunday the army's latest operations made a Security Council resolution all the more pressing. "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. Russia and China, both veto-wielding members of the council, oppose any resolution on Syria. 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.