LONDON — Britain says a third Royal Navy vessel is heading to the Persian Gulf to protect merchant shipping in the Strait of Hormuz.

The navy says the air-defence destroyer Defender, a Type 45 warship, will join the Type 23 Duke-class frigates Kent and Montrose.

The Montrose is due to leave for planned repairs later this month, while the Kent has relieved the air-defence destroyer Duncan.

Britain’s navy has been escorting U.K.-flagged vessels in the region since Iran seized a British-flagged oil tanker there last month.

The navy originally said the Defender was heading to the Asia Pacific region when it left its homeport of Portsmouth alongside the Kent earlier this month.

The change was announced in a Royal Navy statement Saturday.