More than 3,000 Marines and sailors arrived in the Middle East on Sunday in a deployment meant to deter Iran from seizing and harassing merchant ships near the Strait of Hormuz, according to U.S. Naval Forces Central Command.

They came aboard the dock landing ship USS Carter Hall and amphibious assault ship USS Bataan, which together can carry dozens of aircraft, including Ospreys and Harrier jets, plus amphibious landing craft and tactical vehicles.

These forces belong to the Bataan Amphibious Ready Group and 26th Marine Expeditionary Unit (MEU). The North Carolina-based MEU "is capable of conducting amphibious missions, crisis response and limited contingency operations to include enabling the introduction of follow-on forces and designated special operations," according to a release from Naval Forces Central Command.

Defense Secretary Lloyd Austin ordered the move last month "in response to recent attempts by Iran to seize commercial ships" in the Middle East, according to U.S. Central Command.

Iranian officials have pushed back on accounts they "harassed" ships -- claiming in one instance that they were responding to a distress signal, for example.

But according to the Navy, Iran attempted to seize two commercial oil tankers in the Gulf of Oman in July, opening fire on one of them. In May, the U.S. said, Iran seized two merchant ships within one week.

"Since 2021, Iran has harassed, attacked or seized nearly 20 internationally flagged merchant vessels, presenting a clear threat to regional maritime security and the global economy," a Navy release stated in July.

Some Marines of the 26th MEU were flown ahead for training in Bahrain in anticipation of being placed aboard commercial ships traveling through the Strait of Hormuz to stop Iran from capturing them, a U.S. official told ABC News on Friday.

A U.S. official previously said the presence of Marines aboard civilian vessels was expected to be a strong deterrent to Iran. And while their mission would be defensive, the Marines would have the right to defend themselves as necessary, the official said.

The U.S. is considering multiple options and is likely to offer protections to ships that are U.S.-flagged, carrying crews that include U.S. citizens or bringing cargo to or from the U.S., according to the official. The commercial shipping industry has been made aware that this option is or will become available on a voluntary basis.

The U.S. now is waiting for commercial shipping companies to request protection. A senior White House official told ABC News last week that while the plan will likely be approved, no final authorization has been given to U.S. Central Command to go forward.

Pentagon press secretary Brig. Gen. Pat Ryder did not confirm the possibility when asked during a press gaggle on Monday.

"I'm aware of the press reports speculating that that's something we may be looking at doing, but ... I don't have anything to announce," Ryder said.

The ships and troops that arrived this weekend join other U.S. military support recently sent to the area.

"In response to a number of recent alarming events in the Strait of Hormuz, the secretary of defense has ordered the deployment of the destroyer USS Thomas Hudner, F-35 fighters and F-16 fighters to the U.S. Central Command area of responsibility to defend U.S. interests and safeguard freedom of navigation in the region," Pentagon deputy press secretary Sabrina Singh said during a July 17 briefing.