The United States said Thursday it was considering deploying fresh forces to counter Iran, with an official saying some 5,000 to 7,000 troops could head to the region.
Testifying before Congress, John Rood, the under secretary of defense for policy, said the United States was "observing Iran's behavior with concern."
"We're continuing to look at that threat picture and have the ability to dynamically adjust our force posture," Rood told the Senate Armed Services Committee.
Lawmakers appeared frustrated by Rood's answers. Republican Senator Josh Hawley said he wanted to hear from Defense Secretary Mark Esper.
"I'd like to hear from him today on this issue ... I'd like to have it in public because the Pentagon has now made multiple contradictory public statements," Hawley said.
A US official told AFP on condition of anonymity that Esper was considering plans to move between 5,000 and 7,000 troops to the Middle East.
The official did not confirm where the troops would be sent, or in what timeframe, but said that the deployment would be due to frustrations with Iranian-linked groups' attacks on US assets.
Rood, under questioning, denied a report by The Wall Street Journal the United States was considering sending 14,000 more troops -- equivalent to the number sent over the past six months.
Esper also denied the 14,000 figure in a phone call with Senator Jim Inhofe, the chairman of the committee, Pentagon spokeswoman Alyssa Farah said.
Tensions have risen sharply with Iran since US President Donald Trump last year pulled out of a denuclearization pact with Iran and imposed sweeping sanctions, including trying to block all its oil exports.