A second oil tanker owned by the United Kingdom, the Liberian-flagged MV Mesdar, was seized by Iran on Friday, alongside another British one, the Stena Impero.

The order of the seizures, both in the Strait of Hormuz, is currently unknown.

The Stena Impero, which had 23 crew members onboard, “was approached by unidentified small crafts and a helicopter during transit of the Strait of Hormuz while the vessel was in international waters. We are presently unable to contact the vessel which is now heading north towards Iran,” according to Stena Bulk and Northern Marine Management.

It is unknown how many crew members are onboard the MV Mesdar or if anything happened to those onboard the ship, which is owned by Norbulk Shipping.

Norbulk says the ship’s crew are “safe and well,” and can continue their voyage after the vessel was boarded by armed guards.

U.S. President Donald Trump said that the United States will work with the British regarding the seized tankers.

The latest actions come amid ongoing tensions in the region.