Mustard gas tests after IS attack on Iraq military base

The US military is carrying out tests to determine if mustard gas was used in an attack on a base in Iraq.

Islamic State fighters fired a shell into Qaraya West air base in the north of the country, which is being used to prepare for operations aimed at retaking the city of Mosul.

Military personnel who inspected the shell have not shown symptoms of exposure to the chemical agent, an official said.

The remnants of the munition had a black, oily substance on it. Initial tests showed it contained a residue of mustard gas, while a second test came up negative.

A fragment has now been sent for further examination.

A US military official said: "It's been more than 24 hours and we haven't seen anyone who has any indication of blistering or anything like that.

"There are absolutely no injuries. Nobody has been off their typical work schedule. It hasn't impacted the mission in any way."

The US military has repeatedly hit IS' chemical weapons stores in airstrikes, and experts have warned the militants might use the agents in the upcoming Mosul offensive.

But the official described the terror group's technical skills as crude when it came to mounting a chemical weapon attack, and appeared to play down any growing concerns about a threat to US forces.

"We have a moderate level of concern ... on a day to day basis and our concern isn't much greater after seeing this, because it falls into the expected realm," the official said.

Mustard gas can cause severe burns and blisters, as well as damage to the eyes, respiratory system and internal organs.

It was first used in chemical warfare in World War One.

Hundreds of soldiers were reported to have been killed and thousands injured by the agent during the Iran-Iraq war in the 1980s.

Several hundred US troops are at the base, along with Iraqi soldiers.

Iraqi forces retook two villages on the border of Nineveh and Salahuddin provinces from IS on Wednesday as part of a broader operation to secure supply lines ahead of a move on Mosul.

An assault on Mosul is expected to take place in October, but US troops will not be involved in direct fighting on the ground.