Evacuations of embattled eastern Aleppo, which began on Thursday after days of striving to negotiate a cease-fire, have come to a halt.
The Aleppo evacuation was suspended Friday after a report of shooting at a crossing point into the enclave.
The Lebanon-based pan-Arab Al-Mayadeen TV aired images Friday of public green buses reportedly returning evacuees to east Aleppo after the road was closed.
A senior Syrian rebel official from the powerful Ahrar al Sham group involved in the talks said the deal was being held up by Iran and its allied Shi'ite militias who were insisting people be allowed to leave the two besieged Shi'ite villages of Kefraya and al-Foua before letting the Aleppo evacuation happen.
Rebel and government forces agreed Saturday to allow "humanitarian cases" to leave two besieged government-held Shiite villages in northwestern Syria, a step that would allow the resumption of civilian and rebel evacuations from eastern Aleppo which were suspended a day earlier, Hezbollah's media arm and a monitoring group said.
Journalist Zouhir Al Shimale was among about a thousand civilians who were detained by pro-government militias on Friday night when their convoy was stopped as the ceasefire collapsed.
Russia, a key Assad ally, says that more than 6,462 people, including more than 3,000 rebels and 301 wounded, have been taken out. "If these children are not evacuated urgently, they could die", UNICEF said in a statement.
Syria has been locked in a vicious civil war since early 2011, when the Bashar al-Assad regime cracked down on pro-democracy protests - which erupted as part of the "Arab Spring" uprisings - with unexpected ferocity.
The opposition's Britain-based Syrian Observatory for Human Rights said the evacuation of some 4,000 people, including wounded, from the villages could start Saturday.
The observatory cited sources inside Al-Foua, which is located in the rebel-held Idlib province to the west of Aleppo. Putin said Ankara had helped broker the rebel exit from Aleppo now underway.
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"It also said rebels had bombarded a road due to be used by buses to conduct the evacuation from the Shi'ite villages".
More than 2,700 children have left in the past 24 hours, including the sick, wounded and those without their parents, UNICEF said.
It was not immediately clear how long the suspension would last or whether it would delay the ceasefire deal under which the tens of thousands of residents and rebel fighters were being evacuated.
Almost 10,000 civilians and fighters had been bused out of eastern Aleppo by Friday morning, Russian and opposition officials agree.
Members of the World Health Organization (WHO), the International Red Cross Committee and Red Crescent were told to leave the area with buses and ambulances.
The Russians and Syrians claimed to take the responsibility for securing the rebel convoys out of Aleppo. Among them, 65 were in critical condition, he said.
"Well I'm still here - and there are thousands upon thousands of people who are still here".
Turkish President Recep Tayyip Erdogan said he discussed the situation in Aleppo yesterday with U.S. and Russian counterparts Barack Obama and Vladimir Putin.
"Responsibility for this brutality lies in one place alone: with the Assad regime and its allies Russian Federation and Iran".