More than 7,000 people have been evacuated from four besieged towns in the latest co-ordinated population transfer in Syria's six-year civil war.

As diplomacy in Moscow focused on the US air strikes targeting the country, over 2,350 people were taken by bus out of the twin towns of Madaya and Zabadani near Damascus.

Another 5,000 people were evacuated on 75 buses from the northern rebel-beseiged towns of Foua and Kfraya, according to Abdul Hakim Baghdadi, a pro-government interlocutor who helped negotiate the transfer.

"Honestly, when we left Madaya, I felt sadness, anger and sorrow. But now, on the road, I don't feel anything. I feel cold as ice," said Muhammad Darwish.

He was taken out of Madaya, which is besieged by pro-government forces in the mountains west of the capital.

"There was no heating, no food, nothing to sustain our lives. We left so that God willing (the siege) may ease on those who remain," said Ahmad Afandar, 19. His parents stayed behind.

In a video posted on Facebook from one of the buses departing Madaya, a man identified as Hossam said: "We were forced to leave. We left our land, our parents, our memories, our childhood - everything."

He signed off defiantly, however. "I have conviction that we will be back."

Provincial governor Alaa Ibrahim said the government is to restore its control over the towns once it is satisfied that no armed men remain.

Critics have denounced the deal as a forced rearrangement of the country's population, with sectarian overtones.

Through a deft policy of divide and conquer, President Bashar Assad has steered what started as a broad movement against his authority in 2011 into a choice between him and Sunni Islamist rule.

Madaya and Zabadani are believed to now be wholly inhabited by Sunnis. The predominantly Shiite Foua and Kfraya have remained loyal to the Syrian government, while the surrounding Idlib province has come under hard-line Sunni, rebel rule.

The evacuation deal was brokered by Qatar, negotiating on behalf of the rebels, and Iran, on behalf of the government, in March. The United Nations is not supervising the evacuations.

These are the first in a number of evacuations stretching over two months to move some 30,000 Syrians from besieged areas.

Another 3,000 people are expected to be moved out of Foua and Kfraya on Friday evening, according to Mr Baghdadi.

Madaya and Zabadani are the latest in a constellation of towns once held by the opposition around Damascus to submit to government rule.

Pro-government forces have held the two towns under siege for nearly two years. In Madaya, residents were given the option to stay and "reconcile" their status with government authorities.

Military defectors, draft-dodgers and reservists called up will have between six months to a year to return to the armed services, or apply for an exemption. Most of the estimated 40,000 residents will stay and accept the terms.

But at least 2,000 will not, according to Mr Darwish, who was a medical worker in Madaya.