Syria's President Bashar al-Assad has paid tribute to his army and a group of soldiers who escaped an almost month-long rebel siege, in comments which follow a series of regime losses.

Assad, quoted by state news agency SANA late Friday, saluted the "heroism" of some 150 soldiers and their families who were able to escape a hospital building in the town of Jisr al-Shughur in northwestern Syria.

"You represent with your heroism the soldiers of the Syrian army," Assad told their commanding officer, Colonel Mahmud Sabha.

"You resisted because you refused failure or capitulation," Assad said.

"Your life and those of the soldiers of the army and the national defence forces (pro-regime militia) are the most important thing for us and what we try always to protect."

The group had been besieged inside the building in Jisr al-Shughur since the town in Idlib province fell to rebels including Al-Qaeda's local affiliate, on April 25.

On Friday, most of those inside managed to escape just as the hospital was finally overrun by the rebel forces who had surrounded it.

The loss of Jisr al-Shughur came after the fall of the provincial capital Idlib city, and has been followed by a string of other regime setbacks.

The ancient city of Palmyra fell to the Islamic State jihadist group earlier this week and the government now only retains control of its border posts with Lebanon.

More than 220,000 people have been killed in Syria's conflict since March 2011.