Six Jordanian security personnel have been killed in a suicide truck bomb attack near a makeshift refugee camp on the border with Syria, officials say.
The attack took place at about 05:30 (02:30 GMT) in the remote Rukban area.
Hours later, Jordan declared its northern and north-eastern borders would become closed military zones.
It is not yet clear who carried out the attack, but the jihadist group Islamic State (IS) has threatened in the past to “break down” Jordan’s borders.
The kingdom is part of the US-led coalition against IS and has carried out air strikes on militants in Syria.
Tuesday’s attack, the first of its kind since the conflict in Syria began in 2011, saw an explosives-laden truck driven at high speed over the border from Syria and blown up beside a Jordanian military post.