AMMAN, Jordan — Jordan sealed its last entry points for Syrian refugees on Tuesday after a suicide bomber detonated a car bomb in a no-man’s land on the border, killing four Jordanian soldiers, a police officer and a civil defense officer.

The attack took place about 5:30 a.m. on the sand berm marking the frontier between the countries, near a refugee camp where an estimated 60,000 people have been living in harsh conditions.

The Jordanian military said in a statement that the car carrying explosives had struck a military post in the buffer zone at the border after approaching from the refugee camp, and that Jordanian forces opened fire. The vehicle exploded, the statement said, killing the security personnel and wounding 14 others.

The statement, released several hours later by the Jordanian Armed Forces, declared the northern and northeastern borders a military zone and warned that any movement of vehicles or individuals there without permission would be seen as a hostile act.