A team of U.S. military investigators has made an initial assessment that Iran or groups it supports was behind an alleged sabotage attack on 4 tankers in the Gulf of Oman.

President Trump, asked about the incident on Monday, said "it's going to be a bad problem for Iran if something happens."

The White House has ordered a U.S. aircraft carrier strike group and 4 B-52 bombers to the region as tensions with Iran soar.

Images of the ships show little apparent damage, apart from a large hole in one of the tankers, but U.S. officials say each vessel sustained similar damage.

Dubai, United Arab Emirates -- Four oil tankers anchored in the Mideast were damaged by what Saudi and U.S. officials say were "sabotage" attacks, though images of the ships have shown clear visible damage to only one of the vessels. Details of the alleged sabotage to two Saudi, one Norwegian and one Emirati oil tanker on Sunday remained unclear, and none of the nations to which the vessels belong had assigned any blame.

However, on Monday American officials told CBS News senior national security correspondent David Martin that the initial assessment of a U.S. team sent to investigate the incidents was that Iran or Iranian-backed proxies had used explosives to blow holes in the four ships.

The incidents demonstrated the raised risks for shippers in a region vital to global energy supplies as tensions soar between the U.S. and Iran in the wake of President Trump's decision to pull the U.S. out of the nuclear deal agreed by world powers and to impose harsh new sanctions on the Islamic Republic.

Get Breaking News Delivered to Your Inbox

Asked at the White House about the incident on Monday, President Trump responded: "It's going to be a bad problem for Iran if something happens."

Meanwhile, Iran's Foreign Minister Javad Zarif, who is currently holding talks with his counterpart in India, said that the U.S. "has been escalating the situation unnecessarily."

"We do not seek escalation but we have always defended ourselves," he said.

The U.S. had warned sailors of the potential for attacks by Iran or groups it backs on commercial sea traffic just days before the alleged sabotage, and regional allies of the United Arab Emirates condemned the incidents as the tankers were off the coast of the UAE port city of Fujairah.

The U.S. Navy's 5th Fleet, which patrols the Mideast and operates from a base in Fujairah, has repeatedly declined to comment.

The Trump administration has already sent four B-52 bombers to the Persian Gulf to counter alleged, still-unspecified threats from Tehran, and the USS Abraham Lincoln aircraft carrier strike group is also headed for the Gulf.

Spanish ship backs out

On Tuesday, Spain temporarily pulled one of its frigates that's part of a U.S.-led combat fleet from near the Persian Gulf because of mounting U.S.-Iran tensions. The Ministry of Defense said the Méndez Núñez, with 215 sailors on board, would not cross the Strait of Hormuz into the Gulf together with the USS Abraham Lincoln.

The Ministry declined to elaborate on the reasons for the sudden change.

Spanish media, citing government sources, said Spain was concerned that it could be dragged to an unwanted conflict as a result of the crisis between Washington and Teheran surrounding the unraveling nuclear deal.

The Spanish frigate was the only non-U.S. vessel in the fleet.

Damage to ships unclear

The scale of the alleged sabotage remained unclear. A statement from Saudi Energy Minister Khalid al-Falih said two of the kingdom's oil tankers, including one due to later carry crude to the U.S., sustained "significant damage." However, a report from Sky News Arabia, a satellite channel owned by an Abu Dhabi ruling family member, showed the allegedly targeted Saudi tanker Al Marzoqah afloat without any apparent damage.

The oil tankers were visible in satellite images provided Tuesday to the AP by Colorado-based Maxar Technologies. A boom surrounded the Emirati oil tanker A. Michel, indicating the possibility of an oil leak. The other three showed no visible major damage from above.

The MT Andrea Victory, the fourth allegedly targeted ship, sustained a hole in its hull just above its waterline from "an unknown object," its owner Thome Ship Management said in a statement. Images on Monday of the Norwegian-flagged Andrea Victory, which the company said was "not in any danger of sinking," showed damage similar to what the firm described.

Port officials take a photo of the damaged Andrea Victory tanker at the Port of Fujairah, United Arab Emirates, May 13, 2019. REUTERS

A U.S. official told the Associated Press that each ship sustained a 5- to 10-foot hole, near or just below the water line, suspected to have been caused by explosive charges. Emirati officials had requested the team of U.S. military investigators aid them in their probe.

Splash247.com, a shipping and maritime news website, quoted officials at the port in Fujairah as saying "limpet mines" were the suspected weapons used to cause the damage. They are magnetic bombs that can be stuck onto steel-hulled vessels by anyone who can get close enough on a small boat, or by divers in the water.

"Our aim is not war"

Citing heightened tensions in the region, the United Nations called on "all concerned parties to exercise restraint for the sake of regional peace, including by ensuring maritime security" and freedom of navigation, U.N. deputy spokesman Farhan Haq said.

Shortly after the Saudi announcement that two of the country's tankers had been attacked, Iran's Foreign Ministry called for further clarification about what exactly happened with the vessels. The ministry's spokesman, Abbas Mousavi, was quoted by the official IRNA news agency as warning against any "conspiracy orchestrated by ill-wishers" and "adventurism by foreigners" to undermine the maritime region's stability and security. Both the UAE and Saudi Arabia are staunch opponents of Iran's government.

Tensions have risen since Mr. Trump withdrew America from the 2015 nuclear deal between Iran and world powers. Last week, Iran warned it would begin enriching uranium at higher levels in 60 days if world powers failed to negotiate new terms for the deal.

European Union officials met Monday in Brussels to thrash out ways to keep the Iran nuclear deal afloat. U.S. Secretary of State Mike Pompeo had traveled there for talks.

"We're not going to miscalculate. Our aim is not war," Pompeo told CNBC in an interview. "Our aim is a change in the behavior of the Iranian leadership."

Speaking before the Brussels meeting on Monday, Britain's Foreign Minister Jeremy Hunt warned of the risks of an "accident" sparking a conflict between the United States and Iran.

"We are very worried about the risk of a conflict happening by accident with an escalation that is unintended," Hunt said.

Underlying the regional risk, the general-secretary of the six-nation Gulf Cooperation Council described the alleged sabotage as a "serious escalation," and said "such irresponsible acts will increase tension and conflicts in the region and expose its peoples to great danger."