MOSCOW — Escalating a confrontation with Russia, Turkey’s prime minister said Thursday that Russian military equipment and ammunition bound for Syria’s Defense Ministry had been confiscated from a Syrian civilian jetliner on a Moscow-to-Damascus flight, which was forced to land in Ankara on suspicion of illicitly carrying war material.

The accusation by the prime minister, Recep Tayyip Erdogan, also further inflamed Turkey’s already difficult relationship with Syria, where a 19-month-old uprising against President Bashar Assad has expanded into a civil war that is threatening the stability of the Middle East.