Syria's army battled the Islamic State group on the edges of Deir Ezzor Monday, seeking to break the siege of a government enclave and oust the jihadists from a key stronghold.

The jihadist group has already lost more than half of its nearby bastion of Raqa to attacking US-backed forces, and the loss of Deir Ezzor city and the surrounding oil-rich province would leave it with only a handful of isolated outposts.

Deir Ezzor province borders Iraq, where IS has also been expelled from former strongholds Mosul and Tal Afar.

The jihadists hold large parts of Deir Ezzor province, and more than half the provincial capital Deir Ezzor city, the remainder of which is controlled by the government and under IS siege.

Syrian troops have been advancing towards Deir Ezzor city on several fronts, backed by ally Russia, which Monday said two of its soldiers had been killed in the province.

By Monday afternoon, Syrian soldiers were three kilometres (nearly two miles) from the city, the Syrian state television said in a breaking news alert.

"The Syrian army has advanced towards Deir Ezzor to break the siege on it and is now just three kilometres from the city," it said.

The Britain-based Syrian Observatory for Human Rights monitoring group said the troops and allied fighters had arrived at the Brigade 137 base on the western outskirts of the city, and were battling to reach troops besieged by IS inside.

A military source told AFP: "There have been multiple collapses of the Daesh (IS) line in the west of Deir Ezzor province, allowing the army to move quickly."

"The siege on the government troops will be broken within hours."

- 'Best day of my life' -

A 31-year-old teacher inside the regime enclave was ecstatic.

"It's the best day of my life to see the siege coming to an end. It was the heaviest burden on civilians," Uday al-Ali told AFP by phone.

"It's a real day of celebration for the city."

Syrian troops were also some 12 kilometres from Deir Ezzor's besieged military airport, the Observatory said.

Provincial governor Mohamed Ibrahim Samra, quoted by state news agency SANA, spoke of a festive mood in the city.

"Yesterday Deir Ezzor city saw celebrations and rejoicing among all segments of society ahead of the expected victory with the advance of the Syrian Arab Army to the outskirts of the besieged city," he said.

The Russian defence ministry also reported that Syrian forces were advancing on the city, backed by Russian air strikes.

"The fall of IS in Deir Ezzor will be a strategic defeat for the international terrorist group in Syria," it said in a statement.

It later reported two Russian soldiers had been killed by IS artillery fire as their convoy entered Deir Ezzor province, without specifying when the incident took place.

IS seized large parts of the province, including its many oilfields, in mid-2014 as it rampaged across Syria and Iraq.

By early 2015, it had also seized parts of Deir Ezzor city and laid siege to remaining areas under government control.

The siege tightened further earlier this year, when IS advanced and cut the government-held parts of the city in two, with a southern section by the key military airport now divided from a northern sector.

- Humanitarian crisis -

An estimated 100,000 people remain in government-held parts of the city, which had a pre-war population of some 300,000.

The Observatory estimates more than 10,000 people may live in the parts of the city held by IS, although precise information is hard to come by.

The siege has created a humanitarian crisis in the city, with food and medical shortages and soaring prices.

The government has brought supplies in by helicopter, and the United Nations has periodically airdropped humanitarian aid, but the situation remains difficult for those under siege.

Conditions are also reportedly dire for civilians trapped in IS-held parts of the city, with activists reporting food and medical shortages as well as water and electricity cuts.

Syria's army has been advancing towards Deir Ezzor on several fronts in recent weeks, including from the west through neighbouring Raqa province, and from the south via central Homs.

Capturing Deir Ezzor would be a key gain for Syria's government, which has scored a series of military victories in recent months with Russian support.

Government forces have moved quickly towards the city, seeking to head off potential rival advances including by a US-backed Kurdish-Arab alliance that is conducting a separate battle to oust IS from the city of Raqa.

More than 330,00 people have been killed in Syria since the conflict began with anti-government protests in March 2011.

Source: AFP