LONDON- Three Iranian vessels attempted to block the passage of a ship, the British Heritage, through the Strait of Hormuz, but withdrew after warnings from a British warship, the British government said on Thursday.

"HMS Montrose was forced to position herself between the Iranian vessels and British Heritage and issue verbal warnings to the Iranian vessels, which then turned away," a British government representative said in a statement.

The incident happened almost a week after British Royal Marines boarded an Iranian tanker, Grace 1, off Gibraltar and seized it on suspicion that it was breaking sanctions by taking oil to Syria. 

"We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region," the British government representative added.

(Reporting by Bill Schomberg; Writing by Darren Schuettler; Editing by Clarence Fernandez) ((darren.schuettler@thomsonreuters.com; +65 6870 3278;))