BEIRUT (Reuters) - A group monitoring the Syrian war said an army air strike on an Islamic State-controlled town in the north killed at least 28 people including three children on Saturday, though the military denied the report.

The Syrian Observatory for Human Rights, a UK-based organization that monitors the war via a network of activists on the ground, said 19 civilians were among the dead in a helicopter attack on al-Bab, 30 km (20 miles) northeast of Aleppo.

A Syrian military source said the army had not carried out any air strikes in al-Bab on Saturday.

A U.S.-led coalition is waging a separate campaign of air strikes against Islamic State targets in Syria, but rejects the idea of partnering with President Bashar al-Assad, who it sees as part of the problem.

(Writing by Tom Perry; Editing by Andrew Heavens)