President Donald Trump said Iran was responsible for attacks on oil tankers in the Persian Gulf this week, and he vowed that the key shipping lane of the Strait of Hormuz will not be closed.

“Iran did do it, and you know they did it,” Trump said Friday during a phone interview with Fox News. “You saw the boat at night,” he said.

The president’s comments follow American officials’ release of images they said show that Iran was involved in an attack on an oil tanker near the entrance to the Persian Gulf on Thursday, one of two incidents that have raised tensions between the U.S. and the Islamic Republic. Iranian officials have rejected the accusation.

The prospects of a conflict have heightened since the administration tightened its sanctions on Iranian oil exports in early May, following Trump’s decision a year ago to withdraw from the 2015 Iran nuclear accord.

Senior Trump administration officials have said the U.S. is considering a number of responses to the attacks, including the possibility of providing naval escorts to commercial ships traveling through the Strait of Hormuz. An American military response hasn’t been ruled out, they said, and all options are on the table.

U.S. Central Command released a time line of the incident along with video and photographs showing a boat alongside the hull of a larger vessel with a hole in its side. The military said the video showed Iranian forces removing an unexploded limpet mine from from the vessel. Limpet mines are usually attached to a target by magnet.

The video was the first evidence publicly put forward by the U.S. to support its claim -- announced earlier on Thursday by Secretary of State Michael Pompeo -- that Iran was behind the attacks.

“The United States will defend its forces, interests and stand with our partners and allies to safeguard global commerce and regional stability,” Pompeo said, noting that Iran had previously threatened to curtail oil transport in the Strait of Hormuz.

“They’re not going to be closing it,” Trump told Fox News on Friday.

Iranian officials denied any involvement, with Foreign Minister Mohammad Javad Zarif suggesting that Iran’s enemies may have been behind the attacks and reiterating calls for a regional dialogue.

The tanker attacks occurred as Japanese Prime Minister Shinzo Abe was in Tehran meeting officials in what was seen as an effort to help ease tensions between the U.S. and Iran. One of the ships is owned by a Japanese company, according to U.S. officials. Pompeo said the attack was tantamount to Iran insulting Japan as Abe was trying to seek peace.

Trump spoke with Abe on Friday, discussing issues including Abe’s “recent travel to Iran and the circumstances surrounding the attacks on two tankers in the Gulf of Oman,” according to a White House statement. It said Trump thanked Abe “for his effort to facilitate communication with Iran.”

The episode in the Persian Gulf came a day after Iran-backed Houthi rebels in Yemen fired a missile at a Saudi airport, wounding 26 people.