Russian police say a suicide bomber blew himself up in the capital of Chechnya, killing four police officers and wounding four others.

An Associated Press journalist at the scene saw several ambulances leave the site, which has been blocked off by police. The capital of Chechnya, Grozny, was celebrating City Day and the birthday of its pro-Kremlin leader, Ramzan Kadyrov.

Police issued a statement that said policemen operating metal detectors outside a concert hall Sunday evening noticed a suspicious man and when they tried to check his identity he set off the explosives that he was wearing.

After two separatist wars in the 1990s, Chechnya has become more stable under Kadyrov. But a Muslim insurgency still simmers throughout Russia's North Caucasus region, which includes Chechnya.