At least 30 people were killed and dozens of others injured when an air strike by Syrian forces hit a gas station in the north of the country and triggered an explosion.
The blast happened in the town of Ain Issa, about 25 miles (40km) from the Turkish border, said Rami Abdul-Rahman, of the Britain-based Syrian Observatory for Human Rights.
He said witnesses told him they saw at least 30 bodies, but that the death toll was likely to rise. He said dozens of other people were wounded.
Mr Abdul-Rahman quoted one witness as saying that the explosion was caused by an air strike, but that the Observatory could not independently confirm the cause of the blast.
Another group of anti-regime activists, the Local Co-ordination Committees, reported intense attacks by war planes 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 casualties were taken to a hospital in the provincial capital of Raqqa.
Earlier, a Syrian military helicopter crashed near the capital, Damascus.
Syria's Information Ministry said the helicopter went down after its rotor accidentally clipped the tail of a Syrian passenger plane with 200 people on board. The larger aircraft landed safely at Damascus International Airport and no one was hurt, the ministry said.
The air strikes and the close call in the sky underscored the growing turmoil and violence in Syria. The country is embroiled in a civil war between forces fighting for president Bashar Assad and those trying to topple him. More than 23,000 people have been killed in the 18-month conflict, according to activists.
In recent weeks, Mr Assad's regime has stepped up air strikes in northern Syria in an attempt to dislodge rebels from areas they control there.