US Secretary of State John Kerry has arrived in Iraq's capital, Baghdad, as Sunni insurgents expand their control of towns across north-western Iraq.
The Iraqi government appears to have lost control of its western borders after militants reportedly captured crossings to Syria and Jordan at the weekend.
Officials say the rebels, who include Islamic State in Iraq and Syria (ISIS), now control three border crossings in Anbar province, Iraq's largest, on Sunday a day after seizing one at Qaim - a town in the province that borders Syria.
The strategically important airport in the northern town of Tal Afar has also reportedly fallen to the rebels. It controls the main road from the Syrian border to Mosul, Iraq's second biggest city, which was captured by the rebels two weeks ago.
The militants' gains in large parts of western and northern Iraq have alarmed the international community.
In Egypt on Sunday, Mr Kerry warned that ISIS' "ideology of violence and repression is a threat not only to Iraq but to the entire region", the BBC reports.
Mr Kerry is in Baghdad on an unannounced visit to press Iraqi Prime Minister Nouri al-Maliki to form a more inclusive government to quell the Sunni insurgency. He said he would take the same message to other countries during his Middle East tour this week.
In recent days militants have taken four strategically important towns in the predominantly Sunni Anbar province; Qaim, on the Syrian border, and Rutba, Rawa and Anah. Gunmen reportedly captured the border posts of al-Waleed, on the Syrian frontier, and Turaibil, on the Jordanian border, on Sunday after government forces pulled out.
One tribal leader in Anbar told the BBC that the rebel fighters were now in control of 90 percent of the province.
Australia considering new measures
The Australian government is considering new measures to deal with Australians serving with terrorist groups in Syria and Iraq.
It is understood about 150 Australians and dual nationals are fighting overseas, the ABC reports.
Two men identifying themselves as Australians have featured in a recruitment video released by insurgents in Iraq and Syria urging others to join the fight.
Senior ministers have been reviewing border controls and considering giving spy agencies greater access to electronic information.