Kirkuk, Iraq (AFP) – Iraq launched a major operation on Saturday to liberate a jihadist-besieged town, as US Secretary of State John Kerry called for a global coalition to combat the “genocidal” militants.

Saudi Arabia’s King Abdullah warned that the West would be the next Islamic State (IS) target unless swift action is taken, after Britain raised its terror alert level over the threat of jihadist attacks.

The drive to break the more than two-month siege of Amerli came as an NGO said that the IS jihadist group, which has surrounded the Shiite Turkmen-majority town, sold at least 27 women in Syria after kidnapping them in Iraq.

Iraqi security forces, thousands of Shiite militiamen and Kurdish peshmerga fighters are all taking part in the operation to lift the jihadist blockade of Amerli, sources said.

The town has been besieged since IS-led militants launched a major offensive in Iraq in June.

Amerli residents face major shortages of food and water, and are in danger both because of their Shiite faith, which jihadists consider heresy, and their resistance to the militants, which has drawn harsh retribution elsewhere.

The United States began carrying out air strikes against IS in Iraq earlier this month, but has yet to decide if it will expand that military action into the Amerli area, or to Syria.

Army Staff Lieutenant General Abdulamir al-Zaidi said the anti-jihadist operation had been launched with Iraqi air support, and vowed that “we will be victorious over them”.

The operation has retaken 10 villages en route to Amerli, and reinforcements have been airlifted to the town, officials said.

Writing in the New York Times, Kerry urged “a united response led by the United States and the broadest possible coalition of nations” to combat IS.

“What’s needed to confront its nihilistic vision and genocidal agenda is a global coalition using political, humanitarian, economic, law enforcement and intelligence tools to support military force,” he said.

Kerry said he and Defence Secretary Chuck Hagel would meet European counterparts on the sidelines of an upcoming NATO summit to enlist assistance, and then travel to the Middle East to build support “among the countries that are most directly threatened”.

US President Barack Obama has acknowledged that Washington has no strategy yet to tackle IS, which has declared an Islamic “caliphate” in large swathes of territory under its control in Iraq and Syria.

Slavery in Syria

IS has prompted widespread concern because of its sweeping advances in both Syria and Iraq and the killing of hundreds of people, including in gruesome beheadings and mass executions.

It has also sold at least 27 women from Iraq’s Yazidi religious minority for around $1,000 each to fighters in Syria after forcing them to convert to Islam, the Syrian Observatory for Human Rights NGO said.

The group’s progress has also sparked regional fears, with Saudi King Abdullah warning Saturday that “they will reach Europe in a month and America in another month” if left unchecked.

“It is no secret to you, what they have done and what they have yet to do,” he was quoted as telling incoming ambassadors.

“I ask you to transmit this message to your leaders: ‘Fight terrorism with force, reason and (necessary) speed’.”

Britain on Friday raised its terror alert level to “severe”, meaning an attack is “highly likely”, although Washington said it had no plans to follow suit.

The threat from IS is just the latest fallout from Syria’s conflict, which began in March 2011 as a peaceful uprising against President Bashar al-Assad but descended into civil war after his regime responded with a brutal crackdown.

According to the International Organisation for Migration, more than 1.6 million Iraqis have been displaced this year, with more than 850,000 leaving their homes this month alone.The United Nations says that more than 191,000 people have been killed since the Syrian conflict began, and the official number of refugees from more than three years of violence hit three million on Friday.