A source told Rudaw the demonstration was staged against Turkish attacks on Manbij.
Video posted by ANHA news agency showed rising plumes of smoke and people being rushed away in the back of pickup trucks. Other, apparent victims with blood-soaked cloth bandages could be seen walking down a road.
"Cowards and criminals stand behind the bombing of civilians," tweeted Shervan Derwish, spokesperson for the Manbij Miliary Council, saying that Manbij is bigger than this and won't be affected by the "acts of cowards."
The explosion came after a US delegation visited Manbij earlier this week. They met with civilian council and military officials.
Turkey and the United States are currently conducting coordinated but separate patrols which meet at a demarcation line.
US Senator Lindsey Graham said he tried to convince Turkish President Recep Tayyip Erdogan to support a continued US military presence in the northern Syrian city.
“I tried to make the case that you want America in Syria because the outcomes of us leaving are not good,” Graham told Reuters, the news agency reported on Wednesday.
