As Sunni extremists continue to advance in western Iraq, Jordan has bolstered its border security.

Traffic has reportedly thinned and the border crossing technically remains shut in a bid to stop the march by the Islamic State of Iraq and the Levant (Isis) militants.

"The last traffic was around 7:30 pm (1630 GMT) and border officials are saying the situation is not normal on the other side of the border," Minister of State for Media and Communication Mohammad al-Momani told Reuters.

The checkpoints, which are presently controlled by the extremists, on the border serve as the main transit points for all passenger and trade flow between the two countries.

The troops of Jordan, a US ally, have also been deployed along the border amid the heightening tensions in Iraq.

Two key crossings in Anbar were seized by the Isis insurgents over the weekend alongside another strategic area in Qaim bordering Syria.

The capture of the crossings will allow Isis to transfer arms and other supplies to the insurgents fighting against the Shiite-led administration in Iraq.

On the border, police and other security personnel have been given safe passage after they loosely surrendered the frontier posts to avoid bloodletting.

US President Barack Obama has already warned that any spill-over of the conflict to neighbouring countries such as Jordan may have consequences. He told CBS TV network: "We're going to have to be vigilant generally. Their extreme ideology poses a medium and long-term threat."

US Secretary of State John Kerry, who is on a Middle East tour, has visited Jordan and held a meeting with his counterpart Nasser Judeh.

Kerry, expressing concerns that the ongoing conflict threatens the entire region, has insisted all sides should work together to resolve the crisis.