Britain's Defence Secretary Ben Wallace is seen outside Downing Street in London, Britain, August 20, 2019. REUTERS/Hannah McKay

LONDON (Reuters) - Britain is sending another warship to the Gulf to defend freedom of navigation, the defense minister said on Saturday, after Iran seized a British-flagged tanker in the region.

Tensions have risen between Iran and Britain after Iranian commandos seized a British-flagged tanker last month. That came after British forces captured an Iranian oil tanker near Gibraltar, accused of violating sanctions on Syria.

The navy said HMS Duncan, a type 45 frigate, sailed from Britain on August 12, alongside HMS Kent, which was also heading to the Gulf to replace the HMS Duncan.

“Wherever the red ensign flies around the world, the UK stands by to protect freedom of navigation whenever is it tested,” defense minister Ben Wallace said.