Attack wounded five American military personnel and two contractors.

Such attacks were frequent early in war between Israel and Hamas. 

Ain al-Assad base hosts American troops and other personnel.

The United States will not tolerate attacks on American troops in the Middle East, Defense Secretary Lloyd Austin said Tuesday, after rocket fire in Iraq wounded seven US personnel.

The Monday attack was the third in just over three weeks on Ain al-Assad base in western Iraq, which hosts American troops as well as other personnel from the US-led coalition against the Daesh group.

"Make no mistake, the United States will not tolerate attacks on our personnel in the region," Austin told a news conference in Annapolis.

A US defense official said earlier in the day that the attack wounded five American military personnel and two contractors, all of whom are in stable condition.

Such attacks were frequent early in the war between Israel and Hamas Palestinians in Gaza, but until recently had largely halted.

The latest rocket fire comes as fears grow of an attack by Iran and its allies on Israel in retaliation for the killing of top Hamas and Hezbollah figures in strikes either blamed on or claimed by Israel.

The killings are among the most serious series of tit-for-tat attacks that have heightened fears of a regional conflagration stemming from the Gaza war.