The Syrian government has reached a deal for the army to enter a rebel-held region near Damascus and restore the capital's water supply, the provincial governor said Wednesday.

Opposition sources denied there was any such deal, but a source inside the Wadi Barada region reported several hundred civilians were leaving under an agreement.

Wadi Barada, some 15 kilometres (10 miles) northwest of Damascus, provides most of the water to the capital, but mains supplies have been cut since December 22, causing shortages for millions.

President Bashar al-Assad said this week he was determined to retake the area and secure the water supply, and fighting has continued there despite a nationwide truce in place since December 30.

Provincial governor Alaa Ibrahim told state news agency SANA there was now a deal to allow the government to retake control of the region.

"The agreement that was reached in principle requires the militants to give up their heavy weapons and for non-local militants to leave the area of Wadi Barada," he said.

"(Then) the Syrian Arab Army will enter the area to clear it of mines and bombs to prepare for the entry of maintenance teams... to fix the damage caused to the water pumps and pipes by the terrorists' attacks."

But Ahmed Ramadan, an official with the opposition National Coalition, denied any such deal had been reached.

"This information is untrue and is a part of the (regime and its allies') psychological warfare," he told AFP.

The Syrian Observatory for Human Rights, a Britain-based monitor of the war, also said the government had not reached a comprehensive deal with rebels.

But it reported that residents wishing to leave were being offered safe passage on an individual basis.

And a source on the ground in Wadi Barada said Wednesday that some 600 civilians had left, passing through a makeshift tent where government officials were checking documents.

Syria's government accuses rebels, including former Al-Qaeda affiliate Fateh al-Sham Front, of deliberately cutting the supply to the capital.

But the rebels say regime strikes damaged pumping facilities and deny that Fateh al-Sham, previously known as Al-Nusra Front, has forces in the area.

The government has concluded dozens of so-called "reconciliation deals" with rebel-held areas in Syria in recent months, particularly around the capital.

The deals usually offer civilians and rebels safe passage to opposition-held territory elsewhere in exchange for surrendering the area to the army.

The opposition says it is forced into such deals by government sieges and assault, and terms them a "starve or surrender" tactic.