At least 25 buses entered besieged neighborhoods to evacuate rebel fighters and civilians from eastern Aleppo Sunday, Syria's official news agency says — but that was before an attack on buses elsewhere put all movement on hold.

The setback comes after the evacuation effort was halted Friday after just one day, with all sides lobbing accusations at each other.

As the evacuation effort drags on, leaving families and civilians in a dangerous limbo due to both the threat of violence and freezing temperatures, the U.N. Security Council prepares to vote Sunday on a resolution that calls for sending international monitors to the city.

"The resolution was drawn up by France," NPR's Rebecca Hersher reports for our Newscast unit, "and calls on the U.N. to send people into the devastated eastern part of Aleppo to monitor evacuations, and make sure they are voluntary."

The buses that were attacked were slated to help people in two pro-government villages about 35 miles southwest of Aleppo. Under a deal that was reportedly brokered by Iran, Russia and Turkey, some buses and ambulances reached those villages — Kafarya and al-Foua — according to both the Syrian Arab News Agency and the monitoring group the Syrian Observatory for Human Rights.

But then state media and other outlets reported several of the buses had been attacked and burned before they could reach their destination.

"It is not clear which rebel faction attacked the buses, but the area is a stronghold of Al-Qaeda linked forces," NPR's Alison Meuse reports for Newscast.

In another development, Syria's Cabinet will now include an office for the Syrian Arab Red Crescent aid agency, the country's prime minister announced Sunday.

The fall of rebel positions in Aleppo represents both a humanitarian crisis and a key development in Syria's prolonged civil war. But large portions of the country are still being controlled by either rebels, or ISIS, or Kurdish groups.

For a look at the broader picture, here's what Andrew Tabler of the Washington Institute for Near East Policy told NPR's Michel Martin on All Things Considered this weekend:

"It is a turning point. Aleppo is Syria's largest city. The rebels had taken over half of it in the summer of 2012. And controlling a major city in Syria was very important for the rebellion. And their attempt to hold it these last few years became sort of the heart of the revolution in many ways, particularly in the western part of the country. And the taking of Aleppo by the regime is a major setback for the rebels, but it's not going to end the war.

"[Two-thirds] of Syrian territory is outside of Bashar al-Assad's control. Most famously, we have the eastern part of Syria, which is controlled by ISIS, but many of the rebel groups control areas in the northwest, the south. In the northeast, the Kurds and also other Arab tribes control other areas. So Syria's still a fragmented country, and Bashar al-Assad simply just does not have the troops to rapidly retake all those areas. So while Aleppo fell, and it's a victory for Assad, it is not the end of the war. And the dangers that have come out of the Syrian war for Syrians and those in the region and all over the world continue."

As for what to expect from the incoming administration of President-elect Donald Trump in his handling of Syria, Tabler sees two main possibilities.

The first would be that U.S. and Russian military efforts in Syria become better coordinated — and perhaps allow for safe deliveries of aid to the opposition.

The second and more controversial step, Tabler said, could see the U.S. cut off covert aid for rebels in Syria — a move that could also have deep ramifications for U.S. intelligence efforts in the area.

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