ABU DHABI, UNITED ARAB EMIRATES, SEPT. 2 -- The Persian Gulf region today witnessed one of the most intense days of naval warfare in the seven-year-old Iran-Iraq war, with the two belligerents attacking at least seven ships in a 24-hour period.

Iraq said today it had bombed two "large naval targets," or gulf ships, in its renewed campaign of air attacks on Iran's tankers and offshore oil facilities.

Iran had struck five merchant ships in retaliation by this morning. Iranian Prime Minister Mir Hossein Mousavi warned that "blow-for-blow {retaliation} will be followed in a calculated way," according to Tehran radio. {And Thursday morning Iranian gunboats struck a Japanese tanker with three rockets. The Nissan Maru, carrying Iranian oil, continued its trip toward the United Arab Emirates anchorage of Fujahrah, Reuter reported.}

Mousavi said Iran would reject efforts "to impose an American peace on us," a reference to Washington's attempts to pressure Iran into accepting a truce in the war as demanded in a United Nations Security Council resolution.

{Tehran's ambassador to the United Nations, Said Rajaie Khorassani, was quoted by Iran's official Islamic Republic News Agency (IRNA) as saying Iran has not rejected the U.N. resolution because it contains some positive points, Reuter reported. He said Iran is maintaining its position that Iraq should be branded the aggressor in the war, adding that Iran has invited U.N. Secretary General Javier Perez de Cuellar to visit Tehran.}

Despite the escalation in attacks, the damage to gulf shipping has not been severe. There have been no reported casualties among crewmen of the ships hit in recent days, and all of the vessels hit by Iran have continued under their own power with only minor damage.

Iranian seaborne commandos normally use machine guns or rocket-propelled grenades, which tend to cause fires and inflict surface damage but pose no major threat to shipping. Iraqi warplanes, which use air-to-surface missiles in their maritime attacks, normally fly at high altitudes to avoid Iranian antiaircraft fire, and they frequently miss their targets.

Ships that are hit, however, often receive severe damage. Shipping sources quoted by news agencies today said a small supply ship, the 170-foot Big Orange 14, sank in the northern gulf after it was hit by an Iraqi missile during an attack on Iran's Kharg Island oil terminal. No details were available on the fate of the ship's crew.

Gulf shippers, accustomed to high levels of war danger, seemed to respond with unusual alarm to the latest escalation. Journalists who flew over the southern gulf said most of the ships they saw were avoiding normal shipping lanes, while shipping agents in Dubai said other ships had delayed entering the gulf.

After a 45-day lull, Iraq resumed attacks on Iran's tankers and offshore oil facilities after Iran failed to accept the United Nations' July 20 cease-fire call. Iraq has said the attacks were aimed at depriving Iran of oil revenues that Tehran could use to fund its war effort.

Because of the increased danger, Lloyd's of London Underwriters, the leading maritime insurance market, announced a 50 percent rise in war risk premiums for ships entering the gulf, The Associated Press reported.

A military communique from Baghdad, quoted by news agencies, said Iraq bombed a naval target -- the 11th in five days -- off the Iranian coast and set ablaze offshore facilities in Iran's Bahrgan Sar oilfield at the northern tip of the gulf. Iraq said it had continued air raids on land targets. Iraq said all its planes returned safely, while Iran claimed to have shot down two jets.

Iran, which yesterday warned that it would retaliate against Iraq's maritime attacks by bombing Iraqi military and industrial centers, said today its artillery had shelled such targets in southern Iraq, including the southern port city of Basra. Baghdad said an Iranian artillery attack had killed 26 civilians in Basra, Iraq's second-largest city.

At sea, Iran's wave of reprisals included an attack near Dubai this morning on the Greek tanker Dafni. One attack last night, on the South Korean tanker Astro Pegasus, appeared to have been by a larger Iranian naval vessel, believed to be a frigate. The distress call by the Astro Pegasus identified its attacker as a "warship," and journalists who flew over the vessel today said it appeared the ship had been hit by a shell from a 4 1/2-inch gun.

Diplomats here said Arab leaders in the southern gulf were doubtful that the United States could enforce an arms embargo that it has threatened to impose on Iran unless it accepted the U.N. cease-fire call by the end of the week.

"Even if the U.S. gets Moscow to agree to help to enforce an embargo, {such steps} have not been effective so far, and the Arabs doubt that North Korea and China can be made to stop selling," one analyst said. China and North Korea are reportedly among Iran's top arms suppliers.

A European diplomat said the Arab gulf states remain dubious that Washington will make a long-term commitment of its forces, which is why they have been reluctant to offer U.S. forces greater access to their port and military facilities.

{In Washington, Pentagon sources said a U.S. Navy Sea Stallion helicopter involved in mine-hunting operations in the gulf developed mechanical problems Wednesday, forcing the pilot to set down on the water and order three crew members to evacuate, Washington Post staff writer Molly Moore reported.

{Sources said the pilot reported vibrations and a warning light that indicated problems with the aircraft's rotary blade systems, considered a potentially catastrophic malfunction in helicopters. The pilot later was able to take off and land the amphibian craft aboard the helicopter carrier USS Guadalcanal. Pentagon sources said they do not know the cause of the problems.}

Diplomats said the United Arab Emirates has agreed to let the British Navy increase its use of facilities for mine sweepers being sent to the region. "They will be able to increase port visits, fly in more supplies -- everything but store ammunition," one diplomat said.

France ordered three mine sweepers today to the Gulf of Oman, near the mouth of the Persian Gulf and off the emirates' coast.

The diplomats said the emirates have responded favorably to approaches by European governments, but they suggested that the government would be less enthusiastic about stepping up American visits.

"The Arabs remember that the Americans got tired of their commitments in Vietnam and Lebanon, especially when Americans got killed," a diplomat said. "They think a quick solution here is wishful thinking, and they are afraid to appear aligned with the U.S. only to see it pull out and leave them facing an Iran that is angry at them."