A crude oil supertanker caught fire in the Persian Gulf, west of the Strait of Hormuz, prompting a warning from naval authorities in the U.K. for ships in the region to exercise extreme caution. The U.K.’s Maritime Trade Operations said the fire started northwest of Sharjah in the United Arab Emirates. Dispatches in the area said the ship was ablaze about 20 miles off the coast of Sharjah. The cause of the fire was unknown. “There…