LONDON — Apparent attacks on two tankers in the Gulf of Oman on Thursday forced their crews to abandon ship and left one vessel ablaze, a month after four tankers were damaged in the same area, raising alarms about the security of a vital passageway for much of the world’s petroleum.
The early morning incidents, which two shipping companies involved and the White House described as attacks, elevated tensions in a region already unsettled by the escalating conflict between the United States and some of its allies, and Iran.
Frictions have become so intense that other nations have pleaded with all sides to stay calm rather than provoke an all-out war. On Wednesday, Prime Minister Shinzo Abe of Japan, who was visiting Iran and trying to bridge the gap between Iran and the United States, warned of the risk of stumbling into military conflict.
Last month, Jeremy Hunt, the British foreign secretary, said, “We are very worried about the risk of a conflict happening by accident with an escalation that is unintended on either side.”
Sarah Huckabee Sanders, the House press secretary, said Thursday: “The President has been briefed on the attack on ships in the Gulf of Oman. The U.S. Government is providing assistance and will continue to assess the situation.”
It was not immediately clear how the most recent incidents unfolded or who was involved, just as the circumstances of last month’s attacks remain murky. The two ships that were struck on Thursday appeared to have been more seriously damaged than those hit in May.
Iranian officials have denied any involvement in attacks on tankers. But in late May, John Bolton, President Trump’s national security adviser, that Iran was “almost certainly” responsible for the earlier attacks, and Secretary of State Mike Pompeo agreed, saying that they were “efforts by the Iranians to raise the price of crude oil.”
Officials of ther countries have been more cautious about publicly assigning blame. The United Arab Emirates described the attacks as state-sponsored, but did not specify a state.
Saudi Arabia and the U.A.E., both American allies, have long been at odds with Iran, and they are backing opposing sides in the civil war in Yemen. But the sharpest recent changes have been in the United States-Iran relationship.
Mr. Trump has repudiated the 2015 deal limiting Iran’s nuclear program, and he recently moved to cut off Iran’s remaining oil exports and sent additional military forces to the region. In response, Iran recently threatened to block the Strait of Hormuz, the crucial access to the Persian Gulf, and has said it may reduce its compliance with parts of the nuclear pact.
The Houthi faction in Yemen, backed by Iran, has launched attacks recently on targets in Saudi Arabia, including oil pipelines, fueling fears of a wider conflict.
Much of the world’s oil and gas come from the Persian Gulf area, bordered by energy powerhouses like Saudi Arabia, the U.A.E., Iran, Iraq, Kuwait and Bahrain. Some of it leaves the region through pipelines, but a significant portion is carried by ships that must pass through the Strait of Hormuz and the Gulf of Oman. Oil prices rose more than 3 percent on world markets in the hours after the attacks on Thursday.
“We have people of every nationality and vessels of every flat transiting that crucial sea lane every day,” Paolo d’Amico, the chairman of the International Association of Independent Tanker Owners, said in a statement. “We need to remember that some 30 percent of the world’s crude oil passes through the Straits. If the waters are becoming unsafe, the supply to the entire Western world could be at risk.”
Mr. Abe met Wednesday with President Hassan Rouhani of Iran, and Thursday with Ayatollah Ali Khamenei, the supreme leader. He delivered a note from Mr. Trump to Mr. Khamenei, Iranian state media said, but the Ayatollah rebuffed the overture, and said he could not expect honest negotiation from the American administration.
“I do not see Trump as worthy of any message exchange, and I do not have any reply for him, now or in future,” Mr. Khamenei said, according to Iranian media.
Iranian officials suggested that the damage to the tankers was meant to prevent friendly dialogue and provoke aggression. “Suspicious doesn’t begin to describe what likely transpired this morning,” Javad Zarif, the foreign minister, wrote on Twitter.
A government spokesman, Ali Rabiei, warned other nations not to be deceived by those who benefit from instability, Iran’s Labour News Agency reported.
Among American military and intelligence officials in the Persian Gulf region, suspicion immediately fell on possible Iranian complicity.
American analysts were poring over imagery as well as signals intercepts on Thursday to help determine how the attack happened and who was responsible, a senior American official said. Based on the extent of the damage to the tankers, early indications suggested that either mines or torpedoes were used, said the senior official, who acknowledged that the investigation was still in its very early stages.
Last week, Gen. Frank McKenzie, the head of the United States Central Command, told reporters traveling with him in the Middle East that he believed the Iranians or their proxies could carry out an attack at any moment.
“I think the threat is imminent,” General McKenzie told NBC News, without offering specific evidence or other details.
One of the ships disabled on Thursday, the Front Altair, owned by the Norwegian shipping company Frontline, was burning and its crew had evacuated the vessel, according to a shipping industry official who was not authorized to speak for the record. CPC Corporation, the Taiwan oil company that had chartered the ship to carry naphtha, a petroleum product, confirmed that it had been attacked, and a company official told Reuters that a torpedo was suspected.
The Norwegian newspaper VG quoted a Frontline spokesman as saying that its ship was on fire and that all 23 crew members had been rescued. Maritime tracking websites say the Front Altair, registered in the Marshall Islands, had left the Emirati port of Ruwais, headed to Kaohsiung, in Taiwan.
The other tanker, the Panamanian-flagged Kokuka Courageous, was carrying methanol, and the Iranian state news media reported that it, too, was on fire. It was reportedly headed from the Saudi port of Al Jubail to Singapore. Both the ship’s owner and its operator said that all 21 crew members had abandoned ship and were later rescued by a nearby vessel.
“We received a report that our ship was attacked,” Yutaka Katada, the president of the ship’s operator, Kokuka Sangyo, said at a news conference. The crew, all Filipinos, “kept trying to avoid the attacks, but again received an attack three hours later. So crew members left the ship by lifeboats.”
The tanker’s owner, Bernhard Shulte, said in a statement that it had sustained damage to the hull on the starboard side and that one crew member had been slightly injured. The ship “ is not in any danger of sinking,” the company said. “The cargo of methanol is intact.”
Iran’s state news media said the two tankers had been hit by explosions, and confirmed the rescue of 44 mariners. The news channel IRINN said a rescue team from the southern Iranian province of Horozgan had picked up the crew of the ship carrying the Panamanian flag.
Japan’s Trade Ministry said both ships were carrying “Japan-related cargo.”
“We are aware of the reported attack on tankers in the Gulf of Oman,” the United States Fifth Fleet said in a brief statement. “U.S. Naval Forces in the region received two separate distress calls at 6:12 a.m. local time and a second one at 7 a.m.”
The fleet said the U.S.S. Bainbridge, a guided missile destroyer, was “rendering assistance.”
An arm of the British Navy, United Kingdom Maritime Trade Operations, reported that “U.K. and its partners are currently investigating” an incident in the gulf, about 50 miles east of the United Arab Emirates port of Fujairah, but offered no details.