"Ten people were killed and 18 were wounded as a result of a detonation of two explosive devices near the Kawa ring. The first one targeted a bus close to the Saraya bridge in Afrin," the source said, adding that the FSA defused the third explosive device in the city.
Earlier it was reported that a bus departing from the station in front of the city's administration has exploded, killing at least 2 people; 13 more were injured, Turkey's NTV TV channel reported.
Security forces arrived at the scene shortly after the blast. They're asking residents to avoid the area.
An investigation has been launched into the incident.
The explosion occurred on the first anniversary of the end of Operation Olive Branch.
READ MORE: Explosion Heard in Syrian Capital Damascus — Reports
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On 20 January last year, Ankara, jointly with the opposition Free Syrian Army forces, launched Operation Olive Branch in Afrin in order to "clear" Turkey's Syrian border from the terrorist threat. Turkey considers the Democratic Union Party (PYD), a Kurdish political party in northern Syria, and the Kurdish People's Protection Units (YPG) militia to be linked to the Kurdistan Workers' Party (PKK), listed as a terrorist organization by Ankara.
Damascus has condemned the operation as a violation of Syria's sovereignty.