Iranian forces in the Gulf of Oman on Thursday fired a missile at a US drone, hours before an alleged attack by Iran against two tankers in the area.

The surface-to-air missile was fired from a boat and missed its target, a US official told CNN on Friday.

The MQ-9 drone had spotted the Iranian forces approaching the tankers, the official said. He did not say if the aircraft had seen the actual attacks take place.

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The unnamed official added that an American reaper drone had been downed in the Red Sea in the days before the attack, likely by Houthi rebels equipped with an Iranian missile.

Tensions between Washington and Tehran have skyrocketed following the incident.

On Friday, US President Donald Trump blamed Iran for the sabotage, calling the country “a nation of terror” and saying the attack had “Iran written all over it.”

Calling into “Fox & Friends,” Trump said of the Thursday attacks, “Iran did do it.” He cited video purporting to show an Iranian boat removing what the US says is an unexploded mine from one of the vessels.

“You know they did it because you saw the boat,” Trump said. “I guess one of the mines didn’t explode and it’s probably got essentially Iran written all over it.”

Trump cited no new potential US responses, saying the US has been “very tough on sanctions.” He said, “They’ve been told in very strong terms we want to get them back to the table.”

Trump also warned Iran not to close off the strategic Strait of Hormuz, saying if it is closed it won’t be closed for long.

“They’re not going to be closing it. It’s not going to be closed, it’s not going to be closed for long and they know it. They’ve been told in very strong terms,” Trump said.

The US military on Friday released a video it said shows Iran’s Revolutionary Guard removing an unexploded limpet mine from one of the oil tankers, suggesting the Islamic Republic sought to remove evidence of its involvement from the scene.

The black-and-white footage, as well as still photographs released by the US military’s Central Command on Friday, appeared to show the limpet mine on the Japanese-owned Kokuka Courageous.

The ships’ operators offered no immediate explanation on who or what caused the damage against the Norwegian-owned MT Front Altair and the Kokuka Courageous. Each was loaded with petroleum products, and the Front Altair burned for hours, sending up a column of thick, black smoke.

The suspected attacks occurred at dawn Thursday about 40 kilometers (25 miles) off the southern coast of Iran. The Front Altair, loaded with the flammable hydrocarbon mixture naphtha from the United Arab Emirates, radioed for help as it caught fire. A short time later, the Kokuka Courageous, loaded with methanol from Saudi Arabia and Qatar, also called for help. The US Navy rushed to assist the stricken vessels.

While Iran has denied being involved in the attack, Tehran previously used mines against oil tankers in 1987 and 1988 in the “Tanker War,” when the US Navy escorted ships through the region.

Tehran’s foreign minister Mohammad Javad Zarif on Friday fired back at Washington, accusing the US, Israel and Saudi Arabia of a plot to “sabotage diplomacy,” and appeared to insinuate that those countries were behind the assaults.

Iran earlier denied involvement via a statement from its mission to the United Nations.

“The US economic war and terrorism against the Iranian people as well as its massive military presence in the region have been and continue to be the main sources of insecurity and instability in the wider Persian Gulf region and the most significant threat to its peace and security,” the statement said.

Thursday’s attack resembled that of an attack in May targeting four oil tankers off the Emirati port of Fujairah. US officials similarly accused Iran of targeting the ships with limpet mines, which are magnetic and attach to the hulls of a ship. The mines disable, but don’t sink, a vessel.

US Secretary of State Mike Pompeo told journalists on Thursday that the US assessment of Iran’s involvement was based in part on intelligence, as well as the expertise needed for the operation. It was also based on recent incidents in the region, which the US also blamed on Iran, including the use of limpet mines in the Fujairah attack, he said. He also tied Iran to a drone attack by Yemen’s Iranian-backed Houthi rebels on a crucial Saudi oil pipeline around the same time.

Tensions have escalated in the Mideast as Iran appears poised to break the 2015 nuclear deal with world powers, an accord that Trump repudiated last year. In the deal, Tehran agreed to limit its enrichment of uranium in exchange for the lifting of crippling sanctions. Now, Iran is threatening to resume enriching uranium closer to weapons-grade levels if European nations don’t offer it new terms to the deal by July 7.

Already, Iran says it quadrupled its production of low-enriched uranium. Meanwhile, US sanctions have cut off opportunities for Iran to trade its excess uranium and heavy water abroad, putting Tehran on course to violate terms of the nuclear deal regardless.