BAGHDAD -- Al-Qaida-inspired militants pushed deeper into Iraq's Sunni heartland Wednesday, swiftly conquering Saddam Hussein's hometown of Tikrit as soldiers and security forces abandoned their posts and yielded ground once controlled by U.S. forces.
The advance into former insurgent strongholds that had largely been calm before the Americans withdrew less than three years ago is spreading fear that Prime Minister Nouri al-Maliki, struggling to hold onto power after indecisive elections, will be unable to stop the Islamic militants as they press closer to Baghdad.
Fighters from the Islamic State of Iraq and the Levant militant group took control Tuesday of much of Iraq's second-largest city, Mosul, sending an estimated half a million people fleeing from their homes. As in Tikrit, the Sunni militants were able to move in after police and military forces melted away after relatively brief clashes.
The group, which has seized wide swaths of territory, aims to create an Islamic emirate spanning both sides of the Iraq-Syria border.
The capture of Mosul -- along with the fall of Tikrit and the militants' earlier seizure of the western city of Fallujah -- have undone hard-fought gains against insurgents in the years following the 2003 invasion by U.S.-led forces.
The White House said the security situation has deteriorated over the past 24 hours and that the United States was "deeply concerned" about ISIL's continued aggression.
There were no reliable estimates of casualties or the number of insurgents involved, though several hundred gunmen were in Tikrit and more were fighting on the outskirts, said Mizhar Fleih, the deputy head of the municipal council of nearby Samarra. An even larger number of militants likely would have been needed to secure Mosul, a much bigger city.
The militants gained entry to the Turkish consulate in Mosul and held captive 48 people, including diplomats, police, consulate employees and three children, according to an official in the office of Turkish Prime Minister Recep Tayyip Erdogan.
Turkish officials believe the hostages are safe, he said, speaking on condition of anonymity because he was not authorized to comment to reporters on the sensitive issue.
Turkish officials did not make any public comment on the seizure, but the state-run Anadolu Agency reported that Erdogan convened an emergency Cabinet meeting. U.N. Secretary-General Ban Ki-moon strongly condemned the abductions and the seizure of Iraqi territory by the militants, urging "the international community to unite in showing solidarity with Iraq as it confronts this serious security challenge."
"Terrorism must not be allowed to succeed in undoing the path towards democracy in Iraq," Ban said.
While the insurgents have advanced southward, Baghdad did not appear to be in imminent danger from a similar assault, although Sunni insurgents have stepped up car bombings and suicide attacks in the capital in recent months.
So far, ISIL fighters have stuck to the Sunni heartland and former Sunni insurgent strongholds where people are already alienated by the Shiite-led government over allegations of discrimination and mistreatment. The militants also would likely meet far stronger resistance, not only from government forces but by Shiite militias if they tried to advance on the capital.
Mosul, the capital of Ninevah province, and the neighboring Sunni-dominated province of Anbar share a long and porous border with Syria, where the Islamic State is also active.
Mosul's fall was a heavy defeat for al-Maliki. His Shiite-dominated political bloc came first in April 30 parliamentary elections -- the first since the U.S. military withdrawal in 2011 -- but failed to gain a majority, forcing him to try to build a governing coalition.
Al-Maliki said a "conspiracy" led to the massive security failure that allowed militants to capture Mosul, and warned that members of the security forces who fled rather than stand up to the militants should be punished.
He stopped short of assigning direct blame, however, choosing to focus instead on plans to fight back -- without giving specifics.
"We are working to solve the situation," al-Maliki said. "We are regrouping the armed forces that are in charge of clearing Ninevah from those terrorists."
Al-Maliki has pressed parliament to declare a state of emergency over the Mosul attack -- a decision expected later this week.
Iranian airlines cancelled all flights between Tehran and Baghdad due to security concerns, and the Islamic Republic has intensified security measures along its borders, Iran's official IRNA news agency reported.
Shiite powerhouse Iran has strong ties with Iraq's government. Some 17,000 Iranian pilgrims are in Iraq at any given time, the agency quoted Saeed Ohadi, the director of Iran's Hajj and Pilgrimage Organization, as saying.
White House spokesman Josh Earnest warned that the instability was rapidly becoming a humanitarian issue requiring a coordinated response by Iraq's leaders to halt ISIL's advance and wrest territory away from insurgents.
"We condemn ISIL's despicable attack on the Turkish consulate in Mosul, and we call for the immediate release of Turkey's kidnapped diplomatic and security personnel, Earnest said.
Earnest told reporters traveling with President Barack Obama that ISIL poses a "different kind of threat" to American interests than core al-Qaida, which had repeatedly and publicly vowed to attack U.S. soil. Still, he said the U.S. was watching the threat from ISIL "very carefully" because the group has proven itself to be violent and willing to consider attacking U.S. interests and American allies.
Zaineb al-Assam, a Middle East analyst at IHS Country Risk, said ISIL's success in holding onto Mosul would significantly weaken Baghdad's control over Sunni-dominated provinces.
"The objective would be to keep Iraqi security forces off balance, tying them down on passive security duties, as well as to erode (the government's) presence and its ability to sustain services," al-Assam said.
Tikrit residents said the militant group overran several police stations in the Sunni-dominated city. Two Iraqi security officials confirmed that the city, 130 kilometers (80 miles) north of Baghdad and the capital of Salahuddin province, was under ISIL's control and that the provincial governor was missing.
The major oil refinery in Beiji, located between Mosul and Tikrit, remained in government control, the officials said, speaking on condition of anonymity because they weren't authorized to talk to reporters. There were clashes and gunmen tried to take the town but were repelled in a rare success for Iraqi government forces protecting an important facility, the officials said.
In addition to being Saddam's hometown, Tikrit was a power base of his once-powerful Baath Party. The former dictator was captured by U.S. forces while hiding in a hole in the area and he is buried south of town in a tomb draped with the Saddam-era Iraqi flag.
The International Organization for Migration estimated 500,000 people fled the Mosul area, with some seeking safety in the Ninevah countryside or the nearby semiautonomous Kurdish region. Getting into the latter has grown trickier, however, with migrants without family members already in the enclave needing to secure permission from Kurdish authorities, according to the IOM.
Foreign Minister Hoshyar Zebari said Mosul's fall must bring the country's leaders together to deal with the "serious, mortal threat" facing Iraq.
"We can push back on the terrorists ... and there would be a closer cooperation between Baghdad and the Kurdistan Regional Government to work together and try to flush out these foreign fighters," he said on the sidelines of a diplomatic meeting in Athens.
Mosul residents said gunmen went around knocking on doors there Wednesday, reassuring people they would not be harmed. The situation appeared calm but tense, they said.
Violence raged elsewhere in Iraq on Wednesday.
Police and hospital officials said a suicide bomber struck inside a tent where tribesmen were meeting to solve a dispute in Baghdad's Shiite Sadr City neighborhood, killing 31 and wounding 46.
Car bombs in Shiite areas elsewhere claimed another 17 and maimed dozens, officials said, speaking on condition of anonymity because they were not authorized to talk to the media. Car bombs and suicide attackers are favorite tools of the ISIL.
Schreck reported from Dubai, United Arab Emirates. Associated Press Writers Elena Becatoros in Athens, Qassim Abdul-Zahra in Boston, Desmond Butler in Istanbul, Josh Lederman in Washington and Edith M. Lederer at the United Nations contributed to this report.
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