The US said Thursday (December 5th) 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 defence for policy, said the US was "observing Iran's behavior with concern".
"We are continuing to look at that threat picture and have the ability to dynamically adjust our force posture," Rood told the Senate Armed Services Committee.
A US official speaking on condition of anonymity said Defence Secretary Mark 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 the deployment would be due to frustrations with Iranian-linked groups' attacks on US assets.
In September, the US said Iran was responsible for attacks on Abqaiq oil facility in Saudi Arabia, a close US ally and Iran's regional rival.
Riyadh then asked Washington for reinforcements, receiving two fighter squadrons, additional missile defence batteries, and bringing the number of US troops stationed in the kingdom to about 3,000.
The US also has been alarmed by an uptick in attacks on bases in Iraq, where demonstrations triggered by economic discontent also have targeted Iran's regime and its overwhelming influence in Iraq.
"We are lucky no one has been killed. There is a spike in rocket attacks," another US official said.
"It is clearly not the 'Islamic State of Iraq and Syria' (ISIS). Everything is going in the right direction and it is the right range," the official said, contrasting Iranian capabilities with those of ISIS.
Iran-backed militia fingered
Five rockets hit al-Asad air base in Iraq on Tuesday, just four days after US Vice President Mike Pence visited US troops there.
Security sources said they believed Iran-backed Iraqi militia Kataib Hizbullah was responsible.
Two rockets hit al-Balad air base, north of Baghdad, late Thursday, Iraqi security forces said.
Thursday's attack with Katyusha rockets did not cause any casualties or material damage but "came close", a US official said.
Some 5,200 US troops are deployed at Iraqi bases to help Iraqi forces ensure ISIS does not regroup.
The attacks, targeting either bases or the US embassy in Baghdad, have averaged more than one per week over the past six weeks.
"There is a spike in rocket attacks," a second US official said, adding that although they had caused no US casualties and little damage, they were increasingly worrying.
More than a dozen rockets hit al-Qayyarah air base in northern Iraq last month, one of the largest attacks in recent months to hit an area where US troops are based.
There has been no claim of responsibility for the attacks and Washington has not blamed any particular faction.
But US Secretary of State Mike Pompeo has blamed similar attacks on Iran-aligned groups.