Police previously reported three officers and the bomber died in the incident, but a fourth officer was later found dead.
RIA Novosti said the bomber detonated the bomb at 5 a.m. when police stopped his car at a checkpoint outside the city of Khasavyurt.
Authorities said the explosives left a crater four feet deep.
RIA Novosti said the investigative committee has opened a criminal case on terrorism charges, but no one immediately claimed responsibility for the attack.
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