As Iraqi forces battled to retake the northern city of Tikrit from Sunni armed fighters, the insurgents announced the establishment of a "caliphate," referring to the system of rule that ended nearly 100 years ago with the fall of the Ottoman empire.
Al-Qaeda splinter group the Islamic State of Iraq and the Levant (ISIL) distributed an audio recording online Sunday announcing that it will now go by the term "The Islamic State," and declared its chief Abu Bakr al-Baghdadi as "the caliph" and "leader for Muslims everywhere."
In Washington, the Obama administration called on the international community to unite in the face of the threat.
"ISIL'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 ISIL and the advances it has made," State Department spokeswoman Jen Psaki said.
The Iraqi military launched its bid to wrestle back Tikrit, the hometown of former Iraqi dictator Saddam Hussein, on Saturday with a multi-pronged assault spearheaded by ground troops backed by tanks and helicopters. Security officials said the army is coordinating its campaign with the United States.
The predominantly Sunni city, a hotbed of antipathy toward Iraq's Shia-led government, is one of two major urban centers that fell to ISIL earlier this month during their lightning offensive across the country's north and west.
ISIL appeared to have repelled the military's initial push for Tikrit, which is some 80 miles north of Baghdad, and remained in control of the city on Sunday, but clashes were taking place in the northern neighborhood of Qadissiyah, two residents reached by telephone said.
Muhanad Saif al-Din, who lives in the city center, said he could see smoke rising from Qadissiyah, which borders the University of Tikrit. He said many of the ISIL fighters in Tikrit had deployed to the city's outskirts, apparently to stave off the military attack.
Military spokesman Qassim al-Moussawi told reporters Sunday that the military was in full control of the university and had raised the Iraqi flag over the campus.
"The battle has several stages. The security forces have cleared most of the areas of the first stage and we have achieved results," al-Moussawi said. "It is a matter of time before we declare the total clearing (of Tikrit)."
A provincial official reached by telephone confirmed that the ISIL fighters retained control of most of Tikrit, and that the fighting was concentrated in Qadissiyah. He also reported clashes northwest of the city around an air base that previously served as a U.S. military facility known as Camp Speicher.
The official spoke on condition of anonymity because he was not authorized to brief the media.
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.
"The Americans are with us and they are an important part in the success we are achieving in and around Tikrit," al-Bolani told The Associated Press.
Washington has sent 180 of 300 American troops President Barack Obama has promised to help Iraqi forces fight ISIL. The U.S. is also flying manned and unmanned aircraft on reconnaissance missions over Iraq.
Iraq's government is eager to make progress in Tikrit after weeks of demoralizing defeats at the hands of ISIL and allied armed groups. ISIL’s surge across the vast Sunni-dominated areas that stretch from Baghdad north and west to the Syrian and Jordanian borders has thrown Iraq into its deepest crisis since U.S. troops withdrew in December 2011.
More ominously, the insurgent blitz, which prompted Kurdish forces to assert long-held claims over disputed territory, has raised the prospect of Iraq being cleaved in three along sectarian and ethnic lines.
The U.S. has in recent weeks called on Baghdad to create a new, more inclusive government. Taking a position that appeared to clash with the U.S. preference for a united Iraq, Israeli Prime Minister Benjamin Netanyahu on Sunday voiced support for Kurdish independence.
The Kurds have seized on recent sectarian chaos in Iraq to expand their autonomous northern territory to include Kirkuk, which sits on vast oil deposits that could conceivably make the independent state many dream of economically viable.
For embattled Prime Minister Nouri al-Maliki, success in Tikrit could help restore a degree of faith in his ability to stem the insurgent tide. Maliki, a Shia who has been widely accused of monopolizing power and alienating Iraq's Sunni and Kurdish minorities, is under growing pressure to step aside. But he appears set on a third consecutive term as prime minister after his bloc won the most seats in April elections.
The government received a boost with the arrival in Baghdad late Saturday of five Sukhoi 25 warplanes purchased secondhand from Russia. The aircraft is designed to provide close air support to ground forces and to destroy mobile targets.
Iraqi air force commander Lt. Gen. Anwar Hama Amin said the military is "in urgent need of this type of aircraft during this difficult time."
"These jets will enter service within a few days — the coming three or four days — in order to support the units and to fight the terrorist ISIL organization," he said.
ISIL, which already controls vast swaths in northern and eastern Syria amid the chaos of that nation's civil war, aims to erase the borders of the modern Middle East and impose its strict brand of Sharia law.
The ISIL fighters have tapped into deep-seated discontent among Iraq's Sunnis, who largely dominated the country until the U.S.-led overthrow of Saddam brought the Shia majority to power. Since then, Sunnis have complained of discrimination and said they are unfairly targeted by the country's security forces.
Al Jazeera and wire services