Syrian activists say explosion near Turkish border kills 4

This photo provided by Azaz Media Office, a Syrian anti-government activist group, which has been authenticated based on its contents and other AP reporting, shows Syrian citizens and civil defense workers gathering next of burning car at the explosion scene, in Azaz town, north Syria, Wednesday, May 3, 2017. Syrian activists say a large explosion in a northern town along the border with Turkey has killed and wounded several people. (Azaz Media Office via AP) (The Associated Press)

This photo provided by Azaz Media Office, a Syrian anti-government activist group, which has been authenticated based on its contents and other AP reporting, shows a Syrian White Helmet civil defense worker extinguishing a burning car at the explosion scene, in Azaz town, north Syria, Wednesday, May 3, 2017. Syrian activists say a large explosion in a northern town along the border with Turkey has killed and wounded several people. (Azaz Media Office via AP) (The Associated Press)

This photo provided by Azaz Media Office, a Syrian anti-government activist group, which has been authenticated based on its contents and other AP reporting, shows a Syrian White Helmet civil defense worker extinguishing a burning car at the explosion scene, in Azaz town, north Syria, Wednesday, May 3, 2017. Syrian activists say a large explosion in a northern town along the border with Turkey has killed and wounded several people. (Azaz Media Office via AP) (The Associated Press)

Syrian activists say a large explosion in a northern town along the border with Turkey has killed at least four people and wounded many others.

The Britain-based Syrian Observatory for Human Rights says the death toll in the town of Azaz is likely to climb after Wednesday's blast.

Both the Observatory and the activist-run Revolutionary Forces of Syria media office say the explosion is believed to have been caused by a car bomb. Images posted online by the activist-run Azaz Media Center showed a burnt out car and a fire in the area.