John Kerry arrived in Iraq's Kurdish region Tuesday in a US diplomatic drive aimed at preventing the country from splitting apart in the face of Sunni militants pushing towards Baghdad.
Iraq's security forces have managed to retake a crucial border crossing along the frontier with Syria, but were struggling to contain advances by insurgents, led by the Islamic State of Iraq and the Levant (ISIL), who have taken swathes of five provinces north and west of the capital.
The US Secretary of State's unannounced trip to Arbil came a day after he pledged "intense" American support to Iraq to repel the insurgent offensive which has displaced hundreds of thousands of people, alarmed world leaders, and put Prime Minister Nuri al-Maliki under pressure at home and abroad.
Kerry landed in Arbil to urge Iraqi Kurdistan's president Massud Barzani to work to uphold Iraqi cohesion, after Barzani said Iraq was in a "different era" and that Kurds would "determine their future".
Kerry would highlight "the important role that the Kurds can play in helping the central government address... challenges for the benefit of all Iraqis," State Department spokeswoman Jen Psaki said.
The militant offensive has cleared the way for Iraqi Kurds to take control of disputed territory they want to incorporate into their autonomous region over Baghdad's strong objections.
Crucially, their security forces are now responsible for securing the ethnically mixed oil-rich city of Kirkuk in the heart of the disputed territory.
"Now we are living a different era," Barzani told CNN ahead of Tuesday's talks, as he called for Maliki, whom he called "the one responsible for what has happened" in Iraq, to step down.
Pressed on whether Iraqi Kurds would seek independence, Barzani said: "The time is here for the Kurdistan people to determine their future and the decision of the people is what we are going to uphold."
In Baghdad on Monday, Kerry met Maliki and other Iraqi leaders to urge a speeding up of the government formation process following April elections in order to face down the insurgents.
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.
"This is a critical moment for Iraq's future."
Maliki emphasised the danger of the crisis, telling Kerry it "represents a threat not only to Iraq but to regional and international peace".
The meetings came as Sunni insurgents led by ISIL, but including a raft of other groups including loyalists of now-executed dictator Saddam Hussein, seized a strategic northern town, and security forces retook a border crossing with Syria.
Iraqi security forces are struggling to hold their ground, with Maliki's security spokesman saying "hundreds" of soldiers have been killed since the offensive began two weeks ago -- the most specific official information so far on government losses.
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 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.
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.
Elsewhere, 69 detainees were killed in an attack by militants on a convoy transporting them south of Baghdad, with one policeman and eight insurgents also dying in the clashes.
A family of six was also killed on Baghdad's northern outskirts, and five Kurdish security forces members died in a bombing in northern Iraq.
ISIL 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.
It has commandeered an enormous quantity of cash and resources because of the advance, bolstering coffers that were already the envy of militant groups worldwide.
In Brussels, a two-day meeting of foreign ministers from NATO countries begins Tuesday to discuss the situation in Iraq, as well as Ukraine.
US leaders have stopped short of calling for Maliki to go, but there is little doubt that they feel he has squandered the opportunity to rebuild Iraq since American 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.