WASHINGTON — Iran’s Islamic Revolutionary Guard Corps seized at least one British tanker in the Strait of Hormuz on Friday, according to Iranian state media, setting up a new showdown with the West and demonstrating Tehran’s growing boldness as it seeks to challenge the United States and its allies in the strategic waterway.

A Revolutionary Guard statement read on Iranian state television said the British-flagged Stena Impero tanker had been seized in the Persian Gulf.

U.S. officials and shipping reports from the region indicated that a second tanker, the Mesdar, flagged in Liberia but operated by a British company, had also been seized, but that information could not be confirmed.

Both tankers were seen changing course and heading toward Iran as they traveled through the strategic Strait of Hormuz on Friday, according to shipping tracking service MarineTraffic.com. By early Saturday, the Mesdar had changed course again and appeared to have resumed its scheduled journey toward the Saudi port of Ras Tanura.

The Strait of Hormuz is the narrow waterway that controls access to the Persian Gulf, through which a fifth of the world’s oil is moved.

The British government said it was “urgently” seeking further information about both tankers. The operator of the Stena Impero tanker, Stena Bulk and Northern Marine Management, said the vessel was in international waters when it was “approached by unidentified small crafts and a helicopter during transit of the Strait of Hormuz.”

The ship diverted on a course north toward Iran and then contact was lost, the company said.

Britain’s Foreign Secretary Jeremy Hunt said he was “extremely concerned” by the possible seizures.

When asked by journalists in Washington about the latest incidents, President Trump said: “Let’s see what happens.”

Meanwhile, U.S. Central Command said the U.S. has intensified air patrols over the Strait of Hormuz in response to the tanker seizure.

A Central Command spokesman, Lt. Col. Earl Brown, said a small number of additional patrol aircraft are flying in international airspace to monitor the situation. He also said Central Command’s naval arm has been in contact with U.S. ships operating in the area to ensure their safety.

The apparent diversions Friday follow Iran’s threats to retaliate for the seizure of an Iranian tanker by British forces off Gibraltar in July on suspicion of smuggling oil to Syria in violation of European Union sanctions.

If confirmed, however, they mark a wider escalation by Iran in its two-month-old campaign of threats and attacks against U.S. and allied warships and commercial shipping in the vicinity of the Persian Gulf, as Iran seeks to push back against the Trump administration’s imposition of tough new sanctions. Iran has denied U.S. allegations that it is behind most of the attacks.

The new tensions coincide with the arrival in the region of U.S. naval reinforcements aimed at deterring just such attacks against international shipping. Among the U.S. warships that have arrived in the region is the USS Boxer, which brought down an Iranian drone Thursday that had approached dangerously near, according to Trump and the Pentagon.

On Friday, Iranian television aired footage showing drone images of warships that the broadcaster said disproved Trump’s assertion that the U.S. military had destroyed an Iranian drone.

The television station said the footage was provided by the Revolutionary Guard and showed the USS Boxer entering the Strait of Hormuz.

The video also was posted by Iran’s Press TV and included images taken from above what appeared to be a warship, but the veracity of the footage could not immediately be verified.

This latest spike in tensions came almost a month after Iran downed a U.S. drone over the same waterway, prompting Trump to consider launching a military strike against Iran.

Trump said Thursday that the USS Boxer destroyed the drone after it approached within 1,000 yards of the amphibious assault ship. The Pentagon confirmed that the incident took place.

Iran denied, however, that any encounter had occurred between one of its drones and a U.S. warship, insisting that all its drones were accounted for.

“We have not lost any drone in the Strait of Hormuz nor anywhere else,” Deputy Foreign Minister Abbas Araghchi said on his Twitter account. He suggested that the United States may have shot down one of its own drones “by mistake.”

Iran’s top military spokesman also said there had been no incident involving any Iranian drone.

“All Iranian drones that are in the Persian Gulf and the Strait of Hormuz, including the one which the U.S. mentioned, after carrying out scheduled identification and control missions, have returned to their bases,” said Brig. Gen. Abolfazl Shekari, according to Iran’s Tasnim News Agency.

The USS Boxer is part of an amphibious force that includes more than 2,000 Marines from the 11th Marine Expeditionary Unit, which arrived in the region this week. The Trump administration has accused Iran of being behind a string of incidents, including attacks and harassment against commercial shipping, that have contributed to the rising tensions in the region as the United States sets about squeezing Iran with tighter sanctions.

Iran has denied involvement. On Thursday, however, Iran acknowledged that it had seized a United Arab Emirates-based ship that was reported missing last weekend. The Panama-registered Riah was detained because it was suspected to be involved in smuggling, Iran’s Islamic Revolutionary Guard Corps announced Thursday.

The State Department and Pentagon were scheduled to hold a meeting with diplomats Friday to discuss the need for a coalition to protect maritime security around the Strait of Hormuz.

“A multinational effort is needed to address this global challenge and ensure the safe passage of vessels,” the State Department said in a statement.

Associated Press contributed.