Dubai, July 11 -- The British navy said it prevented three Iranian paramilitary vessels from impeding the passage of a British oil tanker in the Strait of Hormuz early Thursday, a day after Iran's president warned of repercussions for the seizure of its own supertanker.

Iran's Revolutionary Guard denied the allegations, saying if it had received orders to seize any ships it would have done so immediately.

The incident came at a time of heightened tensions over Iran's unraveling nuclear agreement with world powers. Iran recently began breaching uranium enrichment limits in response to the Trump administration's withdrawal from the agreement last year and its imposition of sweeping sanctions.

In recent months, the U.S. has dispatched tho...