An U.S. Navy amphibious assault ship and a Marine expeditionary unit transited the Strait of Hormuz this week after the Pentagon already dispatched a carrier strike group and an Air Force B-52 bomber task force to the region amid tensions with Iran.

The amphibious assault ship Kearsarge transited the Strait of Hormuz on Tuesday, bringing with it the 22nd Marine Expeditionary Unit. The sailors and Marines were “outbound,” a U.S. defense official said on background.

The official said that the Kearsarge is now in the Arabian Sea and that it was a scheduled transit. The voyage was unconnected to the threats from Iran, the official added, but the ship is still an asset available to U.S. Central Command as long as it is operating in the region.

The Strait of Hormuz is a key waterway that feeds into the Persian Gulf. The body of water separates Iran and Saudi Arabia and is a major transportation route for oil tankers and military hardware. Iran has threatened in the past to close the strait — the only path into and out of the Gulf.

The Pentagon and the White House warned this weekend that there are “credible threats” that Iran or its proxy forces may be planning to attack American troops in the region.

The guided-missile destroyer McFaul, bottom, the dry cargo and ammunition ship Alan Shepard, center, and the Wasp-class amphibious assault ship Kearsarge transit the Strait of Hormuz. (Mass Communication Specialist 2nd Class Casey Moore/Navy)

“U.S. Central Command requested the additional forces to protect U.S. forces and interests in the region and to deter any aggression," Navy Capt. Bill Urban, a CENTCOM spokesman, said Tuesday in reference to the bomber task force and aircraft carrier group, not the Kearsarge and its Marines.

The possible attacks from Iran include “threats on land and in the maritime,” Urban said. "We are not going to be able to provide detailed information on specific threats at this time.”

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Citing three anonymous U.S. officials, NBC News reported that the specific threats include possible missile attacks by small Iranian ships in the Persian Gulf; attacks in Iraq by Iranian-trained Shiite militias; and attacks against U.S. ships by the Houthi rebels in Yemen.

There also have been concerns that U.S. outposts in Syria, such as the al Tanf garrison, could be vulnerable to Iranian proxy forces.

“Let me be perfectly clear as I reinforce this point: The long-term, enduring, most significant threat to stability in the CENTCOM AOR is Iran and the Iranian regime’s malign, hegemonistic ambitions across the theater and, indeed, globally,” CENTCOM commander Marine Corps Gen. Frank McKenzie said at a Foundation for Defense of Democracies event in Washington on Wednesday.

Two Marines assigned to the 22nd Marine Expeditionary Unit stand watch on the flight deck of the Kearsarge as the ship transits the Strait of Hormuz. (Mass Communication Specialist 3rd Class Kaitlyn E. Eads/Navy)

Iran has for years armed Houthi rebels in Yemen with anti-tank missiles, small arms and ballistic missiles, according to the Pentagon. The U.S. has backed and armed a Saudi-led coalition in that same war.

Kearsarge Amphibious Ready Group is now deployed and operating under the U.S. Navy’s 5th Fleet, which patrols the Middle East waters as part of CENTCOM’s naval component.

The recent deployment of the carrier strike group and bomber task force should send “a clear and unmistakable message to the Iranian regime,” McKenzie told the crowd at the think tank event.

"Any attack on U.S. interests will be met with unrelenting force,” he said.

The increased tensions also come as Iran is expected to announce plans to withdraw from parts of the 2015 nuclear deal this week, one year after the U.S. left the agreement.