WASHINGTON (AP) — The U.S. is sending additional fighter jets and a warship to the Strait of Hormuz and Gulf of Oman to increase security in the wake of Iranian attempts to seize commercial ships there.

The Pentagon said Monday that the USS Thomas Hudner, a destroyer, and a number of F-35 fighter jets will be heading to the area. The Hudner had been in the Red Sea.

Defense officials last week announced the deployment of F-16s to the area over the past weekend, and there have been A-10 attack aircraft there for nearly two weeks in response to the Iranian activity.

The latest deployments come after Iran tried to seize two oil tankers near the strait early this month, opening fire on one of them. The aircraft are intended to give air cover for the commercial ships moving through the waterway and increase the military’s visibility in the area, as a deterrent to Iran.

The U.S. Navy said in both instances the Iranian naval vessels backed off when the USS McFaul, a guided-missile destroyer, arrived on the scene. The Navy said the McFaul remains in the Gulf region to continue protection of the shipping lanes.

Sabrina Singh, a Pentagon spokeswoman, said it is not clear how long the ship and the aircraft will remain in the region.

“In light of this continued threat and in coordination with our partners and allies, the department is increasing our presence and ability to monitor the strait and surrounding waters,” Singh told Pentagon reporters during a briefing.

The U.S. Navy says Iran has seized at least five commercial vessels in the last two years and has harassed more than a dozen others. Many of the incidents have occurred in and around the Strait of Hormuz, the narrow mouth of the Persian Gulf through which 20% of all crude oil passes.