AMMAN, Jordan — Jordan’s state security court convicted four Syrians on Monday of helping Islamic State militants carry out a 2016 car bomb attack that led to the closure of the Syrian-Jordanian border.

The court sentenced one defendant to death and three to life in prison with hard labor.

The cross-border suicide attack, launched in June 2016 from near the Rukban camp for displaced Syrians on the Syrian-Jordanian frontier, killed seven Jordanian border guards. In response, Jordan sealed the border, barring the entry of virtually all Syrians who were fleeing from fighting and were amassing on the border.

The bearded defendants, ranging in age from 20 to 26, were led into the courtroom cage Monday, dressed in jump suits and wearing rubber sandals. Briefly surrounded by reporters, they denied they had ties to IS, though their lawyer later said they had confessed to such an affiliation during interrogation.

At the time of the car bombing, the defendants were living in Rukban, where more than 50,000 displaced Syrians have been trapped for months or years with little access to humanitarian aid.

Jordan is a key partner in the U.S.-led military coalition against IS in Iraq and Syria and has also stepped up a domestic security crackdown on suspected militants and sympathizers.

The June 2016 border closure was followed by arrest sweeps and expulsions of Syrians in response to a December 2016 shooting attack at a Crusader-era castle in Jordan that killed nine Jordanians and a Canadian tourist.

In Monday’s hearing, defendant Najem al-Amor, 21, was convicted of collecting and passing information about Jordan’s military and its procedures in the Rukban area to Islamic State extremists. He was sentenced to death by hanging.

Three defendants were given life in prison after being convicted of helping al-Amor.

Judge Mohammed Afif said the four confessed to receiving monthly payments from IS in exchange for information on Jordan’s military positions on the border.

Jordanian prosecutors also tracked the defendants’ mobile phone exchanges, he said, and found that al-Amor had filmed the attack and given the footage to IS.

Echoing frequent statements by government officials, the judge said Islamic State militants are determined to carry out attacks in Jordan and that they have infiltrated Rukban, among other things, for this purpose.

“The threat of Daesh is continuing at Jordan’s borders and inside the Hashemite kingdom as well,” he said, referring to the militant group by its Arabic acronym. “We are still fighting them.”

A fifth defendant was acquitted of terrorism charges but sentenced to two years in prison for entering Jordanian territory illegally and for involvement in drug trafficking.

Defense lawyer Bashir Oqeileh said the defendants had confessed to IS links, despite their courtroom denials of any affiliation. The lawyer said he did not believe the confessions were extracted by force.

The court’s ruling must be approved by a higher court before the death penalty can be implemented, he added.

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The story has been corrected to show that nine Jordanians, not 11, were killed in a December 2016 shooting attack on a Crusader-era castle in Jordan.