Sunni tribes took control of a border crossing between Iraq and Jordan late on Sunday after Iraq's army pulled out of the area following a clash with rebels, Iraqi and Jordanian intelligence sources said.
The move came after Sunni militants led by the Islamic State in Iraq and the Levant (ISIL) overran posts further north along Iraq's border with Syria, pursuing their goal to form a "caliphate" straddling both countries that has raised alarm across the Middle East and in the West.
It was not immediately clear if the tribesmen's seizure of the Iraqi-Jordanian Turaibil crossing was part of the broader ISIL advance which has also helped the militant group secure supply lines.
Jordanian army sources said their troops had been on a state of alert along the 181 km (112 mile) border with Iraq for several days, to ward off "any potential or perceived security threats".
ISIL is considered the most powerful force among armed groups who seized the Iraqi city of Falluja, just west of Baghdad, and took parts of Ramadi, capital of the western Anbar province, at the start of the year.