The U.S. Navy Monday destroyed two offshore Iranian oil platforms, sank a defending Iranian patrol boat and bombed two Iranian navy frigates. Iran attacked oil facilities off Sharjah and fired on at least two U.S. vessels.

The American attack on the Persian Gulf oil platforms came in retaliation for a mine explosion that tore a hole in an American frigate last week, injuring 10 crewmen.Also Monday, Iran said the United States had entered the Iran-Iraq war, charging that U.S. helicopters supported an Iraqi land offensive in the Faw Peninsula. There was no immediate response from Washington.

The White House said three U.S. warships ships blasted each Iranian platform. No American casualties were reported in the U.S. attacks, and the Iranians fled prior to the shelling, the White House said.

Defense Secretary Frank C. Carlucci said an American helicopter also was fired upon during the raid but was not hit.

One U.S. warship fired missiles at two approaching Iranian jet fighters, but the fighters reversed course and it was unclear whether they were hit, Carlucci said.

He said an Iranian patrol boat fired on the U.S. cruiser Wainwright, which took part in the attack on one of the platforms.

The Wainwright was not hit. He said the U.S. frigate Simpson returned fire and sank the patrol boat.

About seven hours after the oil platform attack, the 310-foot Iranian frigate Sahand "was noticed closing rapidly upon three U.S.

warships," said Dan Howard, the Pentagon's chief spokesman.

The Iranian warship then fired upon three U.S. aircraft on patrol in the Strait of Hormuz, the entrance to the gulf.

The aircraft, A-6 Intruders, "returned fire with two Harpoon missiles and a number of laser-guided bombs. Shortly thereafter, the USS Strauss, a destroyer, engaged the Sahand with an additional Harpoon," Howard said.

He said the Sahand was on fire and "the smoke is so heavy that it's difficult to do a further assessment at this point."

The Defense Department, in a brief statement, said the second Iranian frigate, the Sabalan, was attacked at around 9:40 a.m. EDT, when the ship fired on Intruder attack jets from the carrier Enterprise.

"The aircraft returned fire and hit the Sabalan with a single laser-guided bomb," the Pentagon said.

"As darkness fell, the Sabalan was down by the stern with tugs fore and aft. We do not intend to renew attacks on the Sabalan unless she exhibits further hostile intent," the Pentagon said.

Iran's official Islamic Republic News Agency said the U.S. warships first struck the Sassan platform in the southern gulf at 9 a.m. (1:30 a.m. EDT). Twenty-three minutes later they attacked the Nasr platform at nearby Sirri Island, IRNA said.

An Iranian warship later shelled the Mubarak oilfield off Sharjah, an emirate in the southern gulf, shipping executives said.

Targeted in the attack were the Scanbay drilling rig, the 112,744-ton British tanker York Marine and a storage facility.

The executives, speaking on condition of anonymity, said the York Marine was set afire and that its crew had abandoned the vessel. The Scanbay reported it was under attack by four gunboats, they said.

The Iranians also fired on the press helicopter of the NBC television network, but did not harm the aircraft or its passengers, executives said.

The London-based Lloyd's Shipping Intelligence Unit reported a U.S. tugboat and supply vessel, the Willi Tide, also was fired on off Sharjah but was not hit.

They said unidentified warplanes swooped low over the attacking Iranian boats, chasing them away from the 283-ton vessel, operated by Tidewater Inc. of New Orleans.

Shipping executives later reported Iranian gunboats attacked and set fire to a Cypriot bulk carrier in the Strait of Hormuz.

The freighter, which was not immediately identified, reportedly was carrying fertilizer.

Iran and Iraq have been at war since 1980, and the war has produced repeated attacks on neutral shipping. Last July, the United States reflagged 11 Kuwaiti tankers and gave them U.S. Navy escorts to protect them against Iranian attack.

Tehran Radio, monitored in Cyprus, said U.S. helicopters attacked Iranian troops in southern Iraq "several times" on Sunday.

The Iranian report was issued after Iraq said its troops, led by the Presidential Guard, recaptured Faw. Iran, which seized the peninsula two years ago, denied Iraqi had retaken it.

The White House said Monday the oil platform attacks were "a measured response to Iran's unlawful use of force."

Spokesman Marlin Fitzwater said the United States raided the platforms because Iran was responsible for the "mine attack" on the USS Samuel B. Roberts.

The platforms were manned by Iranian Revolutionary Guards. Fitzwater said they were given several minutes warning, and some were seen leaving.

The White House spokesman said the frigates Simpson and Bagley and the cruiser Wainwright attacked the Sirri platform.

Fitzwater said the destroyers Merril and McCormick and the landing platform ship Trenton attacked the Sassan platform.

The shipping executives said their monitors picked up a radio message about 30 minutes before the attack in which a U.S. warship urged platform workers to evacuate.

The executives said the warning specified the facilities "will be shelled in five minutes."

The Iranians radioed back: "We have no instructions to leave the place."

Eight minutes later, the American warship, which the executives could not identify, said: "We will blast the platform in half a second."

In October 1987, U.S. warships destroyed Rostam, the sister platform to Sassan, after Iran fired a Chinese Silkworm missile into a U.S.-flagged Kuwaiti oil tanker, injuring 18 crewmen.