Syrian government forces advanced Saturday towards the rebel-held town of Jisr al-Shughur, where around 250 regime force members and their families are trapped in a hospital building, a monitor said.

The Syrian Observatory for Human Rights said government troops were now within two kilometres (just over a mile) of where the group has been trapped since rebels seized Jisr al-Shughur in northwestern Idlib province two weeks ago.

"Regime forces and allied fighters are now two kilometres from the hospital and desperately want to save the 250 people besieged inside," said Observatory director Rami Abdel Rahman.

He said there was fierce fighting between rebels and army backed by air strikes as they sought to approach the hospital on Jisr al-Shughur's southeastern outskirts.

Regime forces inside the hospital have been battling rebels to keep them from entering the building.

It remains unclear how much food and ammunition is available to those trapped, and how many of the 250 people inside are civilians.

A group of rebels including Al-Qaeda's Syrian affiliate Al-Nusra Front seized Jisr al-Shughur on April 25, shortly after capturing the provincial capital of Idlib city.

The loss of the town, strategically located near the border with rebel-backer Turkey and alongside the regime stronghold of Latakia province, was a new setback for the government.

Since then, the regime has also lost one of its remaining military bases in the province.

On Wednesday, President Bashar al-Assad pledged that the army would "arrive soon to these heroes trapped in the Jisr al-Shughur hospital".

The same day, government forces began a counteroffensive in the province.

Elsewhere on Saturday, official news agency SANA said at least five civilians were killed and 19 wounded by rebel shelling in northern Aleppo.

- Ravaged by war -

The deaths occurred in the Salaheddin neighbourhood of the government-controlled west of the city.

Once Syria's economic powerhouse, Aleppo has been ravaged by the country's war and is divided between government control in the west and rebel control in the east.

Regime forces regularly carry out air strikes and drop so-called barrel bombs on the rebel side, and opposition fighters often fire rockets into the government side.

In the Qalamun region in the southwest, Lebanon's Shiite movement Hezbollah announced on its Al-Manar television channel that it and Syrian regime forces had taken Al-Nusra Front's largest base in the region, at Sahlet al-Maaysra.

On Tuesday, Hezbollah chief Hassan Nasrallah threatened to expel the insurgents from the area. Since then, the group has taken several positions with regime air support, according to the Observatory and Syrian military sources.

The Qalamun region straddles the Syria-Lebanon border and was a rebel stronghold until a major operation last year by Syrian regime troops backed by Hezbollah.

In Hasakeh province in the northeast, the Observatory said at least 22 Islamic State group fighters were killed in clashes Saturday with Kurdish forces and in air raids by the US-led coalition.

A Pentagon statement said coalition planes carried out 13 air strikes against IS targets near Hasakeh between Friday morning and Saturday morning.

The strikes hit tactical units and destroyed "nine IS fighting positions", 10 vehicles, two heavy machineguns and an armoured car, it said.

Upwards of 200 IS jihadists have been killed in the region since they launched an offensive in February following their defeat at the Kurdish city of Kobane on the border with Turkey.

More than 220,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests that spiralled into a war after a regime crackdown.