"We have an international situation there in the Middle East, it's not a US situation," Patrick Shanahan told reporters, referring to the attacks Thursday on two oil tankers.

"The focus for myself and Ambassador (John) Bolton and Secretary (Mike) Pompeo is to build international consensus to this international problem," he said, referring respectively to the national security advisor and the secretary of state.

Shanahan said that is why the American military released a video which, it claimed, showed a patrol boat of the Islamic Revolutionary Guards, a powerful branch of the Iranian military, pulling alongside one of the tankers to remove an unexploded limpet mine from its hull.

The Pentagon chief left open the possibility of further reinforcing the American military presence in the region, under the US Central Command, or CENTCOM.

"We're making sure that General (Kenneth) McKenzie and the Central Command have the resources and the support that they need," he said.

Shanahan emphasized that "15 percent of the world's oil flows through the Strait of Hormuz," the relatively narrow passage between the Gulf of Oman and the Persian Gulf.

"So we obviously need to make contingency plans should the situation deteriorate," he went on. "But we also need to broaden our support for this international situation."

As tensions grew, the Pentagon last month deployed a warship to the region carrying vehicles, some of them amphibious, and a Patriot missile battery. Earlier it had moved an aircraft carrier to the area in response to what it said were "imminent" threats from Iran.

And late last month, the US announced the deployment of 1,500 additional troops to the Middle East, invoking "persistent threats" to American forces emanating from what the Pentagon said was the "highest level" of the Iranian leadership.

The US presence was further reinforced with reconnaissance aircraft and a squadron of 12 fighter jets.