Britain joined the United States in a maritime security mission on Monday to protect vessels traveling through the Strait of Hormuz after weeks in which Iran has been seizing ships.

“It is vital to secure the freedom for all international shipping to navigate the Strait of Hormuz without delay, given the increased threat,” said British Defence Secretary Ben Wallace, reported Reuters. A fifth of the world’s oil passes through the Strait.

“The deployment of Royal Navy assets is a sign of our commitment to our U.K.-flagged vessels, and we look forward to working alongside the U.S. and others to find an international solution to the problems in the Strait of Hormuz,” he said.

Iran’s Islamic Revolutionary Guard Corps seized the British tanker Stena Impero in the area last month.

No other countries are involved in the American-led mission.