A U.S. official says an American military team's initial assessment is that Iranian or Iranian-backed proxies used explosives to blow large holes in four ships anchored off the coast of the United Arab Emirates.

The official says each ship has a 5-to-10-foot hole in it, near or just below the water line. The U.S. military team assesses that the holes were caused by explosive charges.

The UAE asked the U.S. to help investigate the damage, which Gulf officials have characterized as sabotage.

The official was not authorized to discuss the investigation publicly and spoke on condition of anonymity.

The U.S. has warned ships that "Iran or its proxies" could be targeting maritime traffic in the region, and America has moved additional ships and aircraft into the region.

President Donald Trump warned earlier Monday that Iran would "suffer greatly" if it targeted U.S. interests after Washington deployed an aircraft carrier and more jet fighters at a time of rising tensions with Tehran.

"We'll see what happens with Iran. If they do anything, it will be a very bad mistake," Trump told reporters at the White House. "If they do anything they will suffer greatly."

Washington withdrew last year from a 2015 pact between Iran and global powers aimed at reining in Tehran's nuclear plans. Since then, the United States has ratcheted up sanctions on Iran, saying it wanted to reduce its oil exports to zero.

U.S. Secretary of State Mike Pompeo canceled a trip to Moscow on Monday and instead stopped in Brussels to share information on "escalating" threats from Iran with European allies and NATO officials, the U.S. special representative for Iran said.

The Associated Press and Reuters contributed to this report.