The assailants, who were driving a VAZ-2114 vehicle, fired shots at a group of police officers at the checkpoint, killing one of them.
"As the gunmen were making their getaway, they saw a Maiskoye district police inspector driving toward them, and killed him," the source said.
North Ossetia was the focus of international attention in September 2004, when terrorists seized Beslan's School No.1 killing 331 people including 186 children. The republic neighbors the troubled Chechnya, Ingushetia and Georgia, with which Russia fought a brief war in August.
Ingushetia has seen a marked increase in fighting between federal forces and militants of late. The Russia-based human rights group, the Moscow Helsinki Group, said in late September that the republic was on the verge of civil war as fighting between militants and authorities intensified. It also accused federal authorities of torture and abductions.