Jordanian soldiers from the al-Hussein Bin Talal 40th Armoured Brigade stand to attention during a military ceremony in Qatraneh, some 90km south of the capital Amman, on April 4, 2016.

Jordan’s King Abdullah vowed to hit back “with an iron fist” against attackers who killed six army border guards with a car bomb near the frontier with Syria on Tuesday, a palace statement said.

The kingdom’s army chief of staff announced on Tuesday that Jordan’s northern and northeastern borders with Syria were closed military zones.

The order comes into immediate effect, just hours after six Jordanian border guards were killed in a suicide attack on their military post in a desolate area in the country’s far eastern border area with Syria that also converges with the Iraqi border.

The attack took place at 05:30 AM local Jordanian time after an explosives-laden vehicle blew up a few hundred meters from a camp for Syrian refugees in a desolate area where the borders of Iraq, Syria and Jordan meet, Jordan’s army said.

Jordan’s state TV says called the incident a “cowardly terrorist attack.”