The ceasefire between rebel-backer Turkey and regime-ally Russia was agreed in Idlib -- the last Syrian outpost out of the control of President Bashar al-Assad's forces -- and entered into force on March 6 since when it has largely held.

The defence ministry blamed the rocket attack on "some radical groups in the region," without elaborating further, adding that the army retaliated by hitting specified targets.

The Britain-based Syrian Observatory for Human Rights said the Turkish army suffered casualties when two explosive charges exploded while a Turkish military convoy was passing on the strategic M4 highway.

Ankara hopes the ceasefire will stem a months-long government assault on the jihadist-dominated region, which is home to some three million people.

The observatory said on Tuesday that four regime fighters and a rebel were killed in clashes in southern Idlib.

Nearly a million in Idlib were forced to flee towards the Turkish border during a regime-led offensive underway since December, which killed around 500 civilians.