NATO foreign ministers convene on Tuesday to discuss the Iraq crisis after US Secretary of State John Kerry pledged "intense" support to Baghdad in the fight against militants pushing towards the capital.
Kerry made a surprise visit to Iraq on Monday as Sunni insurgents led by the jihadist Islamic State of Iraq and the Levant, or ISIS, seized a strategic town in the northern part of the country, while security forces retook a border crossing with Syria.
The militant advance has not only put prime minister Nuri al-Maliki under more pressure, but displaced hundreds of thousands and threatened to tear the country apart.
A two-day meeting of foreign ministers from NATO countries begins on Tuesday to discuss the situation in Iraq, as well as Ukraine.
Earlier this month, NATO chief Anders Fogh Rasmussen said the alliance was following events in Iraq "closely", but said he saw no role for it in the conflict.
Kerry, who is expected to attend at least part of the talks in Brussels, met with Maliki and other Iraqi leaders on Monday to urge a speeding up of the government formation process following April elections in order to face down the insurgents.
Watch: Kerry urges political reform in Iraq
Read: Kerry backs Iraq against 'existential' threat
Washington's "support will be intense, sustained, and if Iraq's leaders take the necessary steps to bring the country together, it will be effective," Kerry said at the US embassy in Baghdad's heavily-fortified Green Zone.
"This is a critical moment for Iraq's future," Kerry said.
Maliki also emphasised the danger of the crisis, telling Kerry it "represents a threat not only to Iraq but to regional and international peace."
'Hundreds' of soldiers killed
Iraqi security forces are struggling to hold their ground in the face of militants who have seized major areas of five provinces.
Maliki's security spokesman, Lieutenant General Qassem Atta, said "hundreds" of soldiers have been killed since the offensive began two weeks ago -- the most specific information by the government so far on losses in security ranks.
Iraqi security forces regained control of the Al-Waleed border crossing with Syria on Monday after militants withdrew, officers said -- a rare bright spot amid a series of recent setbacks.
But insurgents were able to overrun the strategic Shiite-majority northern town of Tal Afar and its airport after days of heavy fighting, an official and witnesses said Monday.
Atta said security forces were still fighting in the Tal Afar area, but added: "Even if we withdrew from Tal Afar or any other area, this does not mean that it is a defeat."
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The town, located along a strategic corridor to Syria, had been the largest in the northern province of Nineveh not to fall to militants.
At the weekend, insurgents swept into the towns of Rawa and Ana in Anbar province, west of Baghdad, after taking the Al-Qaim border crossing with Syria.
The government said it made a "tactical" withdrawal from the towns, control of which allows the militants to widen a strategic route to Syria, where they also hold stretches of territory.
As Kerry began his visit, 69 detainees were killed in an attack by militants on a convoy carrying them in Babil province.
One policeman and eight gunmen were also killed in clashes that erupted during the attack in the Hashimiyah area, according to a police captain and a doctor.
Elsewhere, a family of six was killed on Baghdad's northern outskirts, while five Kurdish security forces members died in a bombing in northern Iraq.
Read: Strategic Iraq town Tal Afar, airport fall to Sunni militants
ISIS aims to create an Islamic state incorporating both Iraq and Syria, where the group has become a major force in the rebellion against President Bashar al-Assad.
Washington wants Arab states to bring pressure on Iraq's leaders to speed up government formation, which has made little headway since April elections, and has tried to convince them ISIS poses as much of a threat to them as to Iraq.
ISIS has commandeered an enormous quantity of cash and resources as a result of the advance, bolstering coffers that were already the envy of militant groups around the world.
US leaders have stopped short of calling for Maliki to step down, but there is little doubt that they feel he has squandered the opportunity to rebuild Iraq since US troops withdrew in 2011.
US president Barack Obama has offered to send up to 300 military advisers to Iraq, but has so far not backed air strikes as requested by Baghdad.
The White House said Monday that Iraq has offered legal guarantees to shield US special forces operatives sent to the country as advisers, in a diplomatic note to Washington.
The failure of Iraq's parliament to endorse a Status of Forces deal with Washington led to the complete exodus of all American troops from the country at the end of 2011 -- despite earlier hopes that a US training force would stay behind after the nine-year war.
Many of Obama's political opponents say their exit fostered a power vacuum which ISIS exploited.
Full coverage: Iraq on the brink