Gunmen have killed four people at the offices of the federal drug control agency in the Russian city of Nalchik, in the volatile North Caucasus region.
The gunmen stole a large cache of weapons and set the building ablaze.
Government officials in Nalchik told Russian news agencies that the attackers were Islamic extremists.
Tensions have been high in Nalchik, capital of the Kabardino-Balkaria republic, since Russian authorities closed many of the city's mosques.
According to Russian reports, the group attacked between 0300 and 0600 (0000 and 0300 GMT).
Two guards were killed, as well as a driver and a member of the Russian special forces, before weapons and ammunition were seized.
The gunmen set the building on fire and made off with 36 sub-machine guns and 136 pistols.
The bodies of the four men were found with gunshot wounds, handcuffed together in the building's cellar, local interior ministry officials said.
The officials were quick to blame the attack on Islamic extremists.
Nalchik's police chief said the attack was the work of "an extremist Wahhabist organisation operating in Kabardino-Balkaria", Interfax reported.
Initial suspicion fell on a known local Islamic group, Yarmuk, Russia's RIA news agency said.
The group was held responsible for a previous attack on senior regional crime officials.
The North Caucasus region has been on high alert for attacks by Islamic militants since September's school massacre in Beslan, in the neighbouring republic of North Ossetia.
In response to that attack, officials in Kabardino-Balkaria moved to close down many of Nalchik's mosques in an effort to weaken suspected extremist networks.
Russian Interior Minister Rashid Nurgaliyev has branded the entire North
Caucasus region a "breeding ground for Wahhabism", an austere Saudi branch of Islam that has become synonymous with extremism within Russia.