The United States has asked its troops in Iraq to prepare for a possible "mustard agent" chemical attack by the Islamic State jihadist group. The Pentagon on Thursday asked its 3,500 military personnel in Iraq to be adequately equipped and trained with use of chemical weapon protection suits as evidence emerged that the Islamic extremists have used a mustard agent against Kurdish Peshmerga forces in a mortar attack recently, according to Fox News.

"The commanders in the field are making sure their troops are adequately prepared for the threats they may face," Pentagon Press Secretary Peter Cook told Fox News.

ISIS has reportedly used chemical weapons against Kurdish Peshmerga forces in Iraq and Syria on multiple occasions. It fired a rocket, carrying a suspected mustard agent, at Kurdish forces' positions near the Mosul on Monday, according to BasNews.

"The impact produced considerable yellow smoke at the scene of the attack, leaving one Peshmerga requiring treatment," the Kurdistan Region's Security Council (KRSC) said in a statement on Tuesday.

"We remain deeply concerned with the escalation and delivery method of these attacks, and urgently call on the International Coalition to provide equipment to Peshmerga forces," the KRSC said, according to NRT TV.

The Hague based Organisation for the Prohibition of Chemical Weapons (OPCW) has urged United Nations Security Council (UNSC) to formally request a probe into alleged use of chemical weapons in Iraq by the Islamic State, reported Reuters.