Iraq's security forces have resumed operations with the international coalition to fight "Islamic State of Iraq and Syria" (ISIS) sleeper cells, the US-led global alliance said, after tensions led to a more than three-week pause.

The international coalition on January 5th announced it was freezing its anti-ISIS campaign in Iraq for security reasons after a spate of rocket attacks on bases where its forces are stationed.

The coalition has provided training and air support for Iraqi forces since 2014 to help them beat ISIS, but the pause meant it could not carry out operations or strikes.

On Thursday (January 30th), coalition spokesman Myles Caggins confirmed the pause was over.

"We are resuming our operations with the Iraqi security forces to defeat ISIS remnants," Caggins said.

A source from the Iraqi military also confirmed that joint operations were back under way, and said a formal announcement would be made shortly.

Patriot system approval pending

The US is meanwhile awaiting a green light from the Iraqi government to deploy Patriot missile defence systems to protect US troops from Iranian missile attacks, Pentagon chief Mark Esper said Thursday.

Iran launched 11 missiles at Ain al-Assad, where US troops are stationed, and another at a base in Erbil on January 8th in retaliation for the US killing of Islamic Revolutionary Guard Corps Quds Force commander Qassem Soleimani.

No US troops were killed, but dozens suffered traumatic brain injuries from the explosions, and the US wants to deploy Patriot missiles to better protect the bases, which house some of the 5,200 US military personnel deployed in Iraq.

The Patriot systems are composed of high performance radars and interceptor missiles capable of destroying incoming ballistic missiles in flight.

Questioned Thursday about the delay in deploying the system, Esper told reporters the Iraqi government has yet to give it the go-ahead.

"We need the permission of the Iraqis," he said. "That is one issue. There may be others with regard to placement and things like that."

Gen. Mark Milley, chairman of the Joint Chiefs of Staff, noted that a Patriot battalion is a relatively large organisation, and the mechanics of deploying one to Iraq "will have to be worked out. And that is, in fact, ongoing".