The evacuation of rebel-held eastern Aleppo was delayed on Wednesday and, while a war monitor said the reason was unclear, an opposition official blamed Shi’ite militias allied to President Bashar al-Assad for the hold up.

A ceasefire agreement brokered by Russia, Assad’s most powerful ally, and Turkey ended years of fighting in the city and has given Assad his biggest victory yet after more than five years of war.

Officials in the military alliance fighting in support of Assad could not be reached immediately for comment on why the evacuation was delayed.

However, none had left by dawn, said a Reuters witness waiting at the agreed point of departure. Twenty buses were waiting there with their engines running but showed no sign of moving into Aleppo’s rebel-held eastern districts.

“There is certainly a delay,” said Rami Abdulrahman, director of the Syrian Observatory, a war monitor.

Officials with Aleppo-based rebel groups accused Shi’ite militias backed by Iran of obstructing implementation of the Russian-brokered deal. The pro-opposition Orient TV cited the negotiation committee in eastern Aleppo as saying there was no clear reason why the wounded had yet to be evacuated.

Assad has been backed by an array of Shi’ite militias from across the region in his campaign for Aleppo.

Read More: reuters