The Pentagon is seeking White House approval to send as many as 10,000 more troops to the Middle East to counter potential Iranian threats, according US officials.
No final decision has been made, and it is not clear whether the White House would approve sending all or just some of the requested forces at a meeting on Thursday, the officials told Associated Press.
The move is not in response to any new threat from Iran, but is aimed at reinforcing security in the region, they said. The troops would be defensive forces, and the discussions will include additional Patriot missile batteries, more ships and increased efforts to monitor Iran.
Air Force Col Patrick Ryder, spokesman for the Joint Chiefs of Staff, declined to comment. "As a matter of long-standing policy, we are not going to discuss or speculate on potential or alleged future operations or plans," he said.
The Pentagon request comes as tensions with Iran continue to simmer, and any move to send more forces to the Middle East would signal a shift for President Donald Trump, who has repeatedly emphasised the need to reduce America's troop presence in the region.
US officials have provided few details about possible Iranian threats, but indicated they initially involved missiles loaded on to small Iranian boats. This week officials said the missiles have been taken off the boats near Iran's shore, but other maritime threats continue.
Sending more troops could also raise questions on Capitol Hill. During back-to-back closed briefings for the House and Senate on Tuesday, defence leaders told congressional officials the US does not want to go to war with Iran and wants to de-escalate the situation.
Acting Defence Secretary Patrick Shanahan and Secretary of State Mike Pompeo told legislators the US was seeking to deter, not provoke, Iran, even while accusing Tehran of threatening US interests in the Middle East.
Many in Congress are sceptical of the administration's approach to Iran, questioning whether it is responding to significant new Iranian threats or escalating a situation that could lead to war.
In early May, the US accelerated the deployment of an aircraft carrier strike group to the Middle East and sent four B-52 bomber aircraft to the region. The Pentagon also decided to move a Patriot air-defence missile battery to an undisclosed country in the area.
The Trump administration has withdrawn all non-essential personnel from Iraq, amid unspecified threats the administration said were linked to Iranian-backed militias in the country.
On Sunday, a rocket was fired into Baghdad's heavily fortified Green Zone, landing about a kilometre from the US Embassy compound. There were no injuries and no group claimed responsibility, but the rocket was believed to have been fired from east Baghdad — which is home to Iran-backed Shiite militias.
Some Democrats say Mr Trump is responsible for drawing Iran's ire. Last year he abruptly pulled the US out of the Iran nuclear deal, negotiated during the Obama administration to prevent Iran from nuclear weapons production, without crafting a coherent strategy for how to combat other Iranian behaviour such as supporting extremist organisations. He also has reimposed punishing sanctions that have crippled Tehran's economy, and designated Iran's Revolutionary Guard Corps as a foreign terrorist organisation in April.
"I have yet to see any exhibited strategy," said Democratic congresswoman Abigail Spanberger, a former CIA officer. She said she found many of the administration's recent statements on Iran to be "deeply troubling".