BAGHDAD -- The al-Qaida breakaway group that has seized much of northeastern Syria and huge tracts of neighboring Iraq formally declared the establishment of a new Islamic state on Sunday and demanded allegiance from Muslims worldwide.
With brutal efficiency, the Sunni extremist group has carved out a large chunk of territory that has effectively erased the border between Iraq and Syria and laid the foundations of its proto-state. But the declaration, made on the first day of the Muslim holy month of Ramadan, could trigger a wave of infighting among the Sunni militant factions that formed a loose alliance in the blitz across Iraq and impact the broader international jihadi movement, especially the future of al-Qaida.
The spokesman for the Islamic State of Iraq and Syria declared the group's chief, Abu Bakr al-Baghdadi, as the leader of the new caliphate, or Islamic state, and called on Muslims everywhere, not just those in areas under the organization's control, to swear loyalty to Mr. Baghdadi and support him.
"The legality of all emirates, groups, states and organizations becomes null by the expansion of the caliph's authority and the arrival of its troops to their areas," said the spokesman, Abu Mohammed al-Adnani, in an audio statement posted online. "Listen to your caliph and obey him. Support your state, which grows every day."
Mr. Adnani loosely defined the Islamic state's territory as running from northern Syria to the Iraqi province of Diyala -- a vast stretch of land straddling the border that is already largely under the Islamic State's control. He also said that with the establishment of the caliphate, the group was changing its name to just the Islamic State, dropping the mention of Iraq and Syria.
Muslim extremists have long dreamed of recreating the Islamic state, or caliphate, that ruled over the Middle East, much of North Africa and beyond in various forms over the course of Islam's 1,400-year history.
It was unclear what immediate impact the declaration would have on the ground in Syria and Iraq, though experts predicted it could herald infighting among the Sunni militants who have joined forces with the Islamic State in its fight against Iraqi Prime Minister Nouri al-Maliki and his Shiite-led government.
"Now the insurgents in Iraq have no excuse for working with ISIS if they were hoping to share power with ISIS," said Aymenn al-Tamimi, an analyst who specializes in Islamic militants in Iraq and Syria. "The prospect of infighting in Iraq is increased for sure."
The greatest impact, however, could be on the broader international jihadi movement, in particular on the future of al-Qaida.
Founded by Osama bin Laden, the group that carried out the Sept. 11, 2001, attacks on the U.S. has long carried the mantle of the international jihadi cause. But the Islamic State has managed to do in Syria and Iraq what al-Qaida never has -- carve out a large swath of territory in the heart of the Arab world and control it.
In Washington, the Obama administration called on the international community to unite in the face of the threat posed by the Sunni extremists.
"[ISIS's] strategy to develop a caliphate across the region has been clear for some time now. That is why this is a critical moment for the international community to stand together against [ISIS] and the advances it has made," State Department spokeswoman Jen Psaki said.
President Barack Obama acknowledged Sunday that militants fighting in Syria and Iraq pose a direct threat to the United States because many of them have Western passports that enable them to easily enter the country without visas.
"I think we have been under serious threat my entire presidency, and we have been under serious threat predating 9/11 from those who embrace this ideology," Mr. Obama said on ABC's "This Week."
"We have to improve our surveillance, reconnaissance, intelligence there. Special forces are going to have a role. And there are going to be times where we take strikes against organizations that could do us harm," Mr. Obama said.
"They're gaining strength in some places," Mr. Obama said. "We've seen Europeans who are sympathetic to their cause traveling into Syria and now may travel into Iraq, getting battle-hardened. Then they come back. They've got European passports. They don't need a visa to get into the United States."
The Islamic State's declaration comes as the Iraqi government tries to wrest back some of the territory it has lost to the jihadi group and its Sunni militant allies in recent weeks.
On Sunday, Iraqi helicopter gunships struck suspected insurgent positions for a second consecutive day in the northern city of Tikrit, the predominantly Sunni hometown of former dictator Saddam Hussein. The Iraqi military launched its push to wrest back Tikrit, a hotbed of antipathy toward Iraq's Shiite-led government, on Saturday with a multipronged assault spearheaded by ground troops backed by tanks and helicopters.
The insurgents appeared to have repelled the military's initial push for Tikrit, and remained in control of the city Sunday, but clashes were taking place in the northern neighborhood of Qadissiyah, two residents reached by telephone said.
A provincial official reached by telephone reported clashes northwest of the city around an air base that previously served as a U.S. military facility known as Camp Speicher.
Jawad al-Bolani, a security official in the provincial operation command, said the U.S. was sharing intelligence with Iraq and has played an "essential" role in the Tikrit offensive.
McClatchy Newspapers contributed.