Sunni militants have reportedly captured two key border crossings in Iraq that are close to Syria and Jordan.
The BBC quoted officials, as saying that the rebels had captured the border posts of al-Waleed, on the Syrian frontier, and Turaibil, on the Jordanian border, on Sunday after government forces pulled out.
The capture of frontier crossings could help Isis transport weapons and other equipment to different battlefields.
Since the fall of Mosul in early June, Isis - the Islamic State in Iraq and the Levant - have helped win large areas in the west and north.
They have taken four strategically important towns in the predominantly Sunni Anbar province - Qaim, Rutba, Rawa and Anah - in the last two days.
The focus has shifted partly to Anbar, the vast, mainly Sunni-populated province to the west of Baghdad, an area where the tribes are particularly strong.
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The reported fall of two more border posts, one on the main road to Jordan, and the other to Syria, means that the Iraqi Government has lost control of all its western borders. One tribal leader said that 90 per cent of the province is now in rebel hands.
There are unconfirmed reports that an airport in the strategic northern town of Tal Afar may have also been captured.
The U.S., which pulled out of Iraq in 2011, is deploying some 300 military advisers to Iraq to help in the fight against the insurgents.