The rocket attack Monday was the latest in a series targeting Ain al-Assad base in recent weeks, which hosts American troops as well as other personnel from the US-led coalition against the Islamic State jihadist group.

The Iraqi government's security media unit said in a statement that after "in-depth investigation and witness statements... five people involved in the illegal act were arrested".

The statement did not provide further details on the suspects or whether they were affiliated with any groups.

According to a US defence official "five US service members and two US contractors were injured in the attack," in which two rockets struck the base.

US Defence Secretary Lloyd Austin blamed the attack on "an Iranian-backed Shiite militia group," but said investigations were ongoing to determine which group.

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

There have also been two other recent attacks targeting Ain al-Assad base -- on July 16 and 25.

Monday's rocket attack came at a time of already heightened tensions in the Middle East, with the region awaiting an expected counterattack by Iran on Israel following the killing of Hamas chief Ismail Haniyeh in Tehran last week.

The rocket attack came after US forces carried out a strike in Iraq last week that a US official said targeted combatants who were attempting to launch drones deemed a threat to American and allied troops.

The strike, which Iraqi sources said left four dead, was the first by American forces in Iraq since February.

Attacks against US troops were much more common in the first few months of the Gaza war, when they were targeted more than 175 times.

The Islamic Resistance in Iraq, a loose alliance of pro-Iran groups, claimed the majority of those attacks, saying they were in solidarity with Palestinians.