But acting Defense Secretary Patrick Shanahan denied news reports that plans under consideration call for the deployment of as many as 10,000 more troops, a move that would further rattle frayed nerves in the region.

"What we're looking at, are there things that we can do to enhance force protection in the Middle East?" Shanahan told reporters on a possible further buildup of the US military presence.

"It may involve sending additional troops," he said.

Earlier this month, the administration of President Donald Trump announced the deployment of an aircraft carrier task force as well as B-52 bombers, an amphibious assault ship and a missile defense battery to the Gulf.

The movements have come in response to what the US says are intelligence warnings of a heightened threat to its interests or allies in the Middle East from Iran.

But they have also provoked skepticism among members of Congress who worry that brinksmanship with Tehran could lead to a dangerous miscalculation.

Media reports Wednesday said the Pentagon was mulling adding 5,000 or 10,000 troops to the region, but Shanahan dismissed both figures.

"There is no 10,000 and there is no 5,000. That's not accurate," he said.

Shanahan said he was in regular contact with Marine General Frank McKenzie, who leads US Central Command, which oversees US military operations in the Middle East.

"We talk to CENTCOM all the time," he said.

The acting Pentagon chief said he would brief Trump on Thursday about the situation before the president heads to Japan.

The United States currently has between 60,000 and 80,000 troops deployed in the area covered by CENTCOM, which includes the 14,000 currently on duty in Afghanistan, 5,200 personnel in Iraq and less than 2,000 in Syria.

Earlier in the week, Shanahan said the US response had put the alleged threat posed by Iran "on hold."

"We have deterred attacks based on reposturing of assets -- deterred attacks against American forces," Shanahan told reporters Tuesday after delivering a classified briefing to the full US Congress.

"Our biggest focus at this point is to prevent Iranian miscalculation. We do not want the situation to escalate," he said.