Looking for His glorious appearing! Titus 2:13

Abu Bakr al-Baghdadi, the self-proclaimed leader of the 'Islamic State' stretching across Iraq and Syria, has vowed to lead the conquest of Rome as he called on Muslims to immigrate to his new land to fight under its banner around the globe.

Baghdadi, who holds a PhD in Islamic studies, said Muslims were being targetted and killed from China to Indonesia. Speaking as the first Caliph, or commander of the Islamic faithful since the dissolution of the Ottoman empire, he called on Muslims to rally to his pan-Islamic state.

"Those who can immigrate to the Islamic State should immigrate, as immigration to the house of Islam is a duty," he said in an audio recording released on a website used by the group formerly known as the Islamic State of Iraq and al-Sham.

"Rush O Muslims to your state. It is your state. Syria is not for Syrians and Iraq is not for Iraqis. The land is for the Muslims, all Muslims.

"This is my advice to you. If you hold to it you will conquer Rome and own the world, if Allah wills."

Having claimed the title of "caliph", Baghdadi appealed to "judges and those who have military and managerial and service skills, and doctors and engineers in all fields."

He also called on jihadi fighters to escalate fighting in the holy month of Ramadan, which began on Sunday. "In this virtuous month or in any other month, there is no deed better than jihad in the path of Allah, so take advantage of this opportunity and walk the path of you righteous predecessors," he said. "So to arms, to arms, soldiers of the Islamic s, fight, fight."

In a reflection of the havoc wreaked the past month by the Sunni insurgency led by the group, the United Nations said more than 2,400 people were killed in Iraq in June, making it the deadliest month in the country in years.

Baghdadi's claims to control vast territority have yet to be tested by an Iraqi government counter attack. Many Muslim groups dispute his putative caliphate. However some experts fear his rise could transform the appeal of extremist Islam, partly by harassing social media to build a global following.

Hassan Hassan, an analyst at Abu Dhabi's Delma Institute, wrote that Baghdadi provided the most radical challenge since the emergence of Osama bin Laden and al-Qaeda. "The whispers of support to a caliph in Afghanistan are now replaced by clear words and acts, amplified by social media," he said. "Jihadism has evolved significantly. It is no longer limited to narrow “elitists” who travel to distant countries to wage jihad. Today’s jihad is more sophisticated and individualised and can be waged everywhere."

The Sunni insurgents' advance, which has plunged Iraq into its worst crisis since US troops left in 2011 puts it up against avowed enemies in Shia areas.