Russian police killed two men on Sunday accused of bombing a North Caucasus hydroelectric plant, media reported, just days after President Dmitry Medvedev threatened to sack security officials if there were another attack.

Six masked men, suspected Islamist militants, stormed the Baksanskaya power plant in Kabardino-Balkaria Wednesday, shot dead two guards and set off remote-controlled bombs beside the main generator units, bringing the station to a halt.

Analysts said the attack could signal a change of tactics by rebels in the North Caucasus trying to expand an Islamist insurgency along Russia's southern flank and focus on economic targets — a threat they have long made public.

Medvedev threatened Thursday to sack top security officials if they failed to prevent new attacks on strategic assets in the region. No one took responsibility for the bombing.

Russian news agencies quoted a police spokesman as saying the armed men were killed in a shootout during an attempt to detain them as they drove away in a car.

"The rebels had taken part in a number of serious crimes … including the attack on the Baksanskaya power plant on July 21," the agencies quoted the spokesman as saying.

The Kremlin is struggling to contain an Islamist insurgency in Chechnya, site of two separatist wars since the mid-1990s, Dagestan and Ingushetia where poverty and official abuse of force push some youths right into the hands of the rebels.