Rebels including an Al-Qaeda affiliate stormed a complex in northwestern Syria on Sunday where some 250 regime forces and civilians have been trapped for two weeks, a monitoring group said.
The Syrian Observatory for Human Rights said rebels had entered the hospital complex in the town of Jisr al-Shughur, the rest of which they captured a fortnight ago.
"The fighters this morning stormed the hospital complex on the southwestern edge of Jisr al-Shughur," Observatory director Rami Abdel Rahman told AFP on Sunday.
"They entered one of the buildings and are engaged in heavy fighting with soldiers inside the complex."
He said at least 39 opposition fighters and "dozens" of regime forces had been killed in fighting inside the hospital and also outside Jisr al-Shughur during the army advance.
Abdel Rahman said Sunday's assault began with a car bombing carried out by a member of Al-Qaeda's Syrian affiliate Al-Nusra Front.
It is the first time the rebels have managed to penetrate the complex.
Signup to our newsletter and follow us on Facebook and Twitter!
Among the 250 people holed up inside are around 150 regime troops, including "high-ranking officers", as well as family members and some civil servants, according to Abdel Rahman.
Rebels seized Jisr al-Shughur on April 25, extending their gains in Idlib province where they have also captured the provincial capital and a military base in recent weeks.
Government troops and militia have been battling to reach the hospital to relieve the siege.
They began their counteroffensive on Wednesday, as President Bashar al-Assad pledged those in the hospital would be rescued soon, and on Saturday were around two kilometres (little more than a mile) away, according to the Observatory.
They have been backed by air strikes against the rebels laying siege to the hospital, which state media said had killed "dozens of terrorists".
Late Sunday afternoon, Syrian state television said two local reporters covering the fighting in the area had been wounded by "terrorists targeting" the media reporting on the battle.
It remains unclear how much food and ammunition those holed up inside the hospital complex have left.
More than 220,000 people have been killed in Syria since the conflict began with anti-government protests in March 2011 that spiralled into civil war after a crackdown by security forces.