Washington (AFP) - The US Navy has halted a mission to accompany American-flagged vessels passing through the Strait of Hormuz, the Pentagon said Wednesday, in a sign of reduced tensions in the strategic waterway.

The protection mission had been ordered last week after a Marshall Islands-flagged ship was seized by Iran's Revolutionary Guard forces and a US-flagged vessel was harassed.

The mission came to an end on Tuesday but US warships will remain in the area to conduct "routine maritime security operations," spokesman Colonel Steven Warren told reporters.

The US naval commander in the region "adjusts his mission based on his view of the conditions" and there had been "several days without incident," Warren said.

The order to accompany US-flagged vessels expired on Tuesday and commanders chose not to renew it, he said.

American warships began shadowing US-flagged vessels in the Strait of Hormuz on Thursday, even as US and Iranian diplomats engaged in pivotal negotiations over Tehran's nuclear program.

While US officials would not use the term "escort", naval ships, including the guided-missile destroyer USS Farragut, were meant to keep an eye on US-flagged commercial vessels, following close enough to take action to secure their safe passage.

But US officials insisted the operation did not constitute a full-fledged escort as the warships were not directly next to the commercial vessels and on the same course.

The Pentagon had said the protection mission could be extended to other countries' vessels, including British-flagged commercial ships.

Iranian authorities said the Marshall Islands-flagged Maersk Tigris was confiscated because of a commercial dispute.

The Strait of Hormuz is often described as the world's most important oil export route. About 30 percent of all oil traded by sea moves through the narrow channel, or about 17 million barrels a day.

At its narrowest, the strait is 21 miles (33 kilometers) wide, but the width of the navigable shipping lane in each direction is only two miles -- separated by a two-mile buffer zone.

Strategists have long feared a miscalculation in the crowded channel could trigger a conflict.

In 2011, Iran threatened that it might close the strait in retaliation for tougher international sanctions. That prompted a warning from Washington that US forces would take action to keep shipping lanes open.