Iranian forces boarded a small tanker in international waters for several hours, serving the world a reminder of tensions in the region that flared up last year and embroiled merchant shipping. The Wila was in the Gulf of Oman, roughly 20 miles from the United Arab Emirates, when it was boarded for about five hours late Wednesday afternoon, according to a U.S. government official with knowledge of the matter. It navigated the Strait of Hormuz, a choke-point for about one-third of the world’s seaborne oil on its way out of the Persian Gulf, ship-tracking data compiled by Bloomberg show.

Two Iranian ships were in the vicinity of the Wila, a Liberian-flagged chemicals and oil-products tanker, when personnel roped down from helicopters, the U.S.-led coalition force International Maritime Security Construct said in a statement.

“Maritime harassments are really the only stick with which Iran can beat its opponents,” said Munro Anderson, a partner at maritime security firm Dryad Global. “It has few levers of influence and treads a fine line when it antagonizes states in the region and the U.S.”