Amateur video appears to show a massive explosion launched by the Free Syrian Army in Idlib province.
The video, which can not be independently verified by Reuters comes as Syria prepares for elections in early June. Government foes dismiss the election as a farce.
With international powers deadlocked over how to resolve the conflict, fighting rages across the country.
Rights groups say more than 200 people are killed every day.
More than 150,000 people have died in the rebellion against President Bashar al- Assad which began with peaceful protests more than three years ago before descending into civil war.
