WASHINGTON (AP) — A U.S. warship on Thursday destroyed an Iranian drone in the Strait of Hormuz after it threatened the ship, President Donald Trump said. The incident marked a new escalation of tensions between the countries less than one month after Iran downed an American drone in the same waterway and Trump came close to retaliating with a military strike.

In remarks at the White House, Trump blamed Iran for a “provocative and hostile” action and said the U.S. responded in self-defense. Iran’s foreign minister, Mohammad Javad Zarif, told reporters as he arrived for a meeting at the United Nations that “we have no information about losing a drone today.”

The clash in one of the busiest waterways for international oil traffic highlighted the risk of war between two countries at odds over a wide range of issues. After Trump pulled the United States out of the Iran nuclear deal last year and imposed additional economic sanctions, the Iranians have pushed back on the military front, allegedly sabotaging Saudi and other oil tankers in the Gulf, shooting down a U.S. drone on June 20 and stepping up support for Houthi rebels in Yemen.

Adding to the economic pressure on Tehran, the Treasury Department said Thursday it was imposing sanctions on what it called a network of front companies and agents involved in helping Iran buy sensitive materials for its nuclear program. It said the targeted individuals and entities are based in Iran, China and Belgium.

Trump said the Navy’s USS Boxer, an amphibious assault ship, took defensive action after the Iranian aircraft closed to within 1,000 yards of the ship and ignored multiple calls to stand down.

“The United States reserves the right to defend our personnel, facilities and interests and calls upon all nations to condemn Iran’s attempts to disrupt freedom of navigation and global commerce,” Trump said.

The Pentagon said the incident happened at 10 a.m. local time Thursday in international waters while the Boxer was transiting the waterway to enter the Persian Gulf. The Boxer is among several U.S. Navy ships in the area, including the USS Abraham Lincoln, an aircraft carrier that has been operating in the nearby North Arabian Sea for weeks.

“A fixed-wing unmanned aerial system approached Boxer and closed within a threatening range,” chief Pentagon spokesman Jonathan Hoffman said in a written statement. “The ship took defensive action against the UAS to ensure the safety of the ship and its crew.”

Neither Trump nor the Pentagon spelled out how the Boxer destroyed the drone. CNN reported that the ship used electronic jamming to bring it down rather than hitting it with a missile.

The Iranians and Americans have had close encounters in the Strait of Hormuz in the past, and it’s not unprecedented for Iran to fly a drone near a U.S. warship.

In December, about 30 Iranian Revolutionary Guard vessels trailed the USS John C. Stennis aircraft carrier and its strike group through the strait as Associated Press journalists on board watched. One small vessel launched what appeared to be a commercial-grade drone to film the U.S. ships.

Other transits have seen the Iranians fire rockets away from American warships or test-fire their machine guns. The Guard’s small fast boats often cut in front of the massive carriers, running dangerously close to running into them in “swarm attacks.” The Guard boats are often armed with bomb-carrying drones and sea-to-sea and surface-to-sea missiles.