Secretary of State John Kerry promised "intense and sustained" U.S. support for Iraq on Monday, but warned that the divided country would only survive if its leaders took urgent steps to unite it.
Hours before Kerry arrived in Baghdad where he made the statement, Sunni tribes — which have joined armed group The Islamic State of Iraq and the Levant (ISIL) in a takeover of northern Iraq — seized the only legal crossing point into Jordan, security sources said, leaving troops with no presence along the entire western frontier which includes some of the Middle East's most important trade routes.
The diplomatic visit comes as the U.S. ponders its next move to help stabilize the sectarian strife-torn nation. President Barack Obama has offered up to 300 American advisers to Iraq, but has held off granting Prime Minister Nuri al-Maliki's Shia Muslim-led government's request for air strikes to counter the two-week advance by armed Sunni groups. Meanwhile, Obama has upped the pressure on Maliki to reform the nation’s governance to include more disaffected Sunni groups and raised the prospect that it .
The insurgency has been fuelled in part by a sense of marginalization and persecution among Iraq's Sunnis.
"The support will be intense and sustained and if Iraq's leaders take the necessary steps to bring the country together, it will be effective," Kerry told reporters in Baghdad.
He said Maliki had "on multiple occasions affirmed his commitment to July 1" as the date to start the formation of a new government bringing in more Sunnis and Kurds to share power.
Iraqi and Jordanian security sources said tribal leaders were negotiating to hand the Turabil desert border post to ISIL, which took two main crossings with Syria in recent days and has pushed the Shia-led government's forces back toward Baghdad.
Iraqi state television said late on Monday that the army had recaptured both the crossing with Jordan and the al-Waleed crossing with Syria.
Ethnic Kurdish forces control a third border post with Syria in the north, leaving government troops with no presence along Iraq's 500-mile western border.
Kerry said: "Iraq faces an existential threat and Iraq's leaders have to beat that threat with the incredible urgency that it demands. The very future of Iraq depends on choices that will be made in the next days and weeks."
Washington, which withdrew its troops from Iraq in 2011 after an occupation that followed the 2003 invasion which toppled dictator Saddam Hussein, has been struggling to help Maliki's administration contain a Sunni insurgency led by ISIL, an Al-Qaeda offshoot which seized northern cities this month.
Washington is worried Maliki and fellow Shia who have won U.S.-backed elections have worsened the insurgency by alienating moderate Sunnis who once fought Al-Qaeda but have now joined the ISIL revolt. While Washington has been careful not to say publicly it wants Maliki to step aside, Iraqi officials say such a message was delivered behind the scenes.
There was little small talk when Kerry met Maliki.
The meeting lasted one hour and 40 minutes, after which Kerry was escorted to his car by Iraq's Foreign Minister Hoshiyar Zebari. As Kerry got in, he said: "That was good."
Iraqis are due to form a new government after an election in April. Maliki's list won the most seats in parliament, but will still require allies to secure a majority.
The need to battle the Sunni insurgency has put the U.S. on the same side as its enemy of 35 years, Iran, which has close ties to the Shia parties that came to power in Baghdad after U.S. forces toppled Saddam.
However, Iran's Supreme Leader Ayatollah Khamenei made clear on Sunday that a rapprochement would not be easy.
"We are strongly opposed to U.S. and other intervention in Iraq," IRNA news agency quoted Khamenei as saying. "We don't approve of it as we believe the Iraqi government, nation and religious authorities are capable of ending the sedition."
Al Jazeera and wire services