Several thousand people have been evacuated from four besieged towns in Syria under a deal between the government and rebels.
People from the north-western towns of Foah and Kefraya were taken to government-held areas near Aleppo.
Evacuees from rebel-held Madaya and Zabadani, near Damascus, were bussed to Idlib province.
It is hoped that more than 30,000 people will be moved under the deal to end a grave humanitarian crisis.
Last month, the UN described the situation in the four towns as "catastrophic", with more than 64,000 civilians "trapped in a cycle of daily violence and deprivation".
Many people are reported to have died as a result of shortages of food or medicine.
Meanwhile, in Moscow, the foreign ministers of Russia, Iran and Syria pledged to investigate a suspected chemical attack in Syria earlier this month that the West has blamed on the Syrian government.
But Syrian President Bashar al-Assad has already said reports of a chemical attack committed by his forces were "100% fabrication".
'A difficult feeling'
Mohammad Darwish, who lived in Madaya, was a dentistry student in Damascus when the conflict began but for the past two years was one of just two medics treating about 40,000 residents.
He left his hometown today and sent the BBC this message: "It's a difficult feeling to leave your homeland, your memories, your families, your country. All negative feelings, we have it now."
Foah and Kefraya, most of whose residents are Shia Muslims, have been encircled by rebels and al-Qaeda-linked Sunni Muslim jihadists since March 2015.
Madaya and Zabadani, which are predominantly Sunni, have meanwhile been besieged since June 2015 by the Syrian army and fighters from Lebanon's Shia Muslim Hezbollah movement.
As part of what is known as the "Four Towns Agreement", the warring parties have allowed the UN and the Red Cross to deliver aid on a few occasions in the past two years and to remove limited numbers of sick and injured people.
The evacuation deal was brokered by Iran, an ally of Mr Assad's government, and Qatar, which supports the rebels. But critics say it amounts to forced demographic change.
Some 4.7 million people live in hard-to-reach and besieged areas in Syria, including 644,000 in UN-declared besieged locations.
The meeting in Moscow on Friday between Russian, Iranian and Syrian foreign ministers was the first held between the three allies since the US launched a missile attack on a Syrian airbase in response to the alleged chemical attack.
Russian Foreign Minister Sergei Lavrov said there was evidence that the suspected attack was "staged". He said Russia, Iran and Syria would conduct an "exhaustive, objective and impartial" investigation.
He also said the three allies were unanimous in considering the US missile strikes on Shayrat airbase "an act of aggression".
The alleged chemical attack targeted the rebel-held town of Khan Sheikhoun, and killed more than 80 people, including many children.