The explosion went off in the town of Ain Issa, about 25 miles (40 kilometers) from the Turkish border, said Rami Abdul-Rahman of the Britain-based Syrian Observatory for Human Rights. Abdul-Rahman said witnesses told him they saw at least 30 bodies, but that the death toll was likely to rise. He said dozens of people were wounded.
Abdul-Rahman quoted one witness as saying the blast was caused by an airstrike, but that the Observatory could not independently confirm the cause of the explosion.
Another group of anti-regime activists, the Local Coordination Committees, reported intense attacks by warplanes on the gas station.
The group did not give a death toll, saying only that many people were killed or wounded. It said more than 70 wounded people were taken to a hospital in the provincial capital of Raqqa.