Syrian state television showed footage of what it claims are mass graves containing the bodies of government security personnel killed by armed gangs. Viewers may find some of the images in this video disturbing.
Syrian security forces say they have retaken Jisr al-Shughur after army troops, backed by helicopter gunships and tanks, moved into the northern town.
Residents who fled the army assault spoke out on Monday, saying troops had begun fighting among themselves in the midst of the military operation.
"The troops are divided. Four tanks defected and they began to fire on one another," said 35-year-old Abdullah, who fled Jisr al-Shughur on Sunday and crossed the border into Turkey in order to find food.
"When they started to fire on each other, I decided to flee," the AFP news agency quoted him as saying.
Abdullah, who like many other refugees would only give his first name, said that the troops had pounded the town with heavy gunfire at the start of the assault.
State television said army units fought "armed groups" on Sunday, but residents and activists said troops had clashed with mutinous soldiers defending the town alongside residents.
"Army divisions entered Jisr al-Shughur and purged the state hospital of armed groups," the television said.
"Two members of the armed organisations were killed, large numbers of them arrested, and lethal weapons in their possession were seized."
A reporter for the Associated Press news agency said the army was in full control of Jisr al-Shughur.
Troops and tanks had laid siege to the town after authorities said the would retaliate against the reported killings of 120 security personnel last week.
Residents who fled to Turkey told AP that thousands of young men, including soldiers and police who switched sides and joined the uprising against President Bashar al-Assad, had armed themselves and planted dynamite at the town entrances.
'Protecting their families'
Jamil Saeb, a resident, told Al Jazeera that tens of people were injured as they tried to protect their properties and their families.
"These people of the committees that are formed among the citizens were facing the armed forces. We're lawyers, employees, pharmacists, from many of the civil professions in the city, trying to face and combat the armed forces."
A Syria-based rights activist, Mustafa Osso, said advancing troops, using tanks, artillery and helicopters gunships, had been fighting against hundreds of army defectors from the area.
"This is the biggest and most dangerous wave of defections'' since an uprising against Assad's government began in mid-March, Osso said.
Osso said there were army operations in three parts of Idlib province including the towns of Maarat al-Numan, Jisr al-Shughur, and the nearby Jabal al-Zawiya, a mountain that includes several villages.
State television reported on June 6 that security personnel had been killed in an ambush, but refugees and rights groups said those killed were mutinous soldiers, shot for refusing to fire on civilians protesting against Assad's one-party rule.
Several testimonies from defected soldiers have emerged in the last week, suggesting a split within the security forces.
Troops on Sunday removed 10 uniformed bodies from a mass grave in front of the military police building. At least four of the bodies were beheaded or struck on the head with an axe, according to an Associated Press reporter who was invited to accompany the Syrian forces.
In-depth coverage of escalating violence across Syria
Earlier, a resident told the Reuters news agency that the army was using up to 150 tanks and armoured vehicles in the town, 20km from Turkey.
"Jisr al-Shughur is small and there is not even space to park all this armour. The shelling is non-stop now. Two helicopters are flying overhead and firing their machine guns," he said over the phone, speaking from a hill overlooking the town.
"Most people have escaped towards Turkey. I heard that a small group of army defectors may have remained because they felt that they had to defend the honour of Jisr al-Shughur, but they must be martyrs by now."
Metin Corabatir, a spokesman for the UN refugee agency, UNHCR, told Al Jazeera that 5,051 Syrians had so far crossed the border to escape violence.
Al Jazeera speaks to a resident in Jisr al-Shughur
about the situation there on Sunday
The refugees are crossing the border through unofficial border crossings.
For now, the Syrian army is totally absent in the border area, a Turkish soldier guarding the frontier said. "In
14 months I have not seen a single soldier on the other side of the border," he told AFP.
Witnesses said up to 10,000 had taken shelter among trees near the border since forces moved into the northwestern province of Idlib.
The crackdown and the resultant misery heaped on civilians trapped in the ongoing violence have been globally condemned.
Human-rights groups say security forces have killed more than 1,300 Syrian civilians in bloody efforts to suppress demonstrations, now in their third month, calling for Assad's removal, political freedom and an end to corruption and poverty.
The US accused the Syrian government on Saturday of creating a "humanitarian crisis" and called on it to halt its offensive and allow immediate access by the International Committee for the Red Cross to help refugees, detainees and the wounded.