Iran "almost certainly" planted mines in the Gulf of Oman to try to impede the most recent convoy of reflagged Kuwaiti tankers and escorting U.S. naval warships, Pentagon officials said yesterday.

Harbor officials yesterday briefly closed part of an anchorage off the port of Fujairah in the Gulf of Oman where several mines have been found since a U.S.-operated supertanker hit a mine in the area Monday. Mine-sweeping crews from four nations reportedly searched an area which, until this week, was considered safe from the dangers of the 7-year-old war between Iran and Iraq.

The area was reopened after no further mines were found, the Los Angeles Times reported.

"We believe that it is . . . almost certainly the Iranians who left those mines there," said Defense Department spokesman Robert B. Sims, "presumably in hopes of placing them in front of our most recent tanker-escort group."

Sims said, however, "We don't have specific evidence of that."

Pentagon officials said their assumptions are based on evidence that the mines found in the Gulf of Oman are the antiquated type of spiked, spherical mine the supertanker Bridgeton struck during the first U.S. escort mission through the Persian Gulf. Mine-hunting crews later found about seven more mines in the same vicinity, off Farsi Island, a base for the Iranian Revolutionary Guard.

Earlier yesterday, a Saudi Arabian coast guard vessel was damaged and two crewmen were slightly wounded when it hit a mine at the northern end of the Persian Gulf, Saudi police reported.

The new infusion of mines in shipping channels of the Persian and Oman gulfs normally free of the weapons has alarmed shipping officials and spurred the United States and several European and gulf nations to expand their mine-sweeping efforts. Iranian officials have accused the United States of laying the mines in the Gulf of Oman and offered to assist in the hunting operations.

"It {mining} is affecting all countries in the region, all shipping in countries that use those waterways," Sims said yesterday.

Two American oil companies, Mobil Oil. Corp. and Chevron Corp., ordered their tankers not to move within 25 miles of the coast near Fujairah, a United Arab Emirates port, shipping officials in the region told The Associated Press.

U.S. warships and reflagged Kuwaiti tankers had been assembling near the port to begin trips through the Strait of Hormuz, within range of Iranian antiship missile sites.

The number of mines spotted in the Gulf of Oman has ranged from four to six, and one was first identified by an ABC News crew from its helicopter.

While tanker activity in the oil-rich region has remained active throughout the mine scare, some shipping officials said yesterday the average number of vessels near the Strait of Hormuz has dropped substantially. Some maritime insurance companies have raised their rates significantly.

The United States has escorted three convoys so far -- two into the Persian Gulf to load up on oil, and one out. Three tankers, in addition to the damaged Bridgeton, are now being loaded with petroleum cargoes for the trip back out of the Persian Gulf.

The British and French governments have decided to send mine-sweepers, and the U.S. Navy's most sophisticated mine-hunters, eight Sea Stallion helicopters, are en route to the Persian Gulf aboard the USS Guadalcanal. The helicopter carrier's departure from Diego Garcia Island in the Indian Ocean was delayed by mechanical problems earlier this week, Sims said.