Russian police have besieged an apartment block in the North Caucasus town of Nalchik in an attempt to arrest a high-profile Islamist militant.
Officials say that Muslim Atayev, who is suspected of leading an attack on the local anti-drug agency, might be hiding in one of the flats.
In the December attack, militants killed four policeman and seized a large amount of firearms.
Several rebels and Mr Atayev's wife and child are said to be in the flats.
Local journalist Zaurbek Shakhmurzayev told BBCRussian.com that the five-storey apartment and adjacent buildings have been evacuated.
Police say Mr Atayev and the other rebels refused to surrender when the building was surrounded by Interior Ministry special forces on Tuesday evening
The siege is said to be part of a planned clampdown on the Yarmuk Jamaat group, which the authorities have blamed for the December attack.
The group was operating in the Kabardino-Balkaria autonomy, of which Nalchik is the capital. The authorities say it was a part a radical Islamist network operating in Russia's volatile North Caucasus region and linked to Chechen rebels.
In the last few years, Islamist militants conducted a number of attacks in the North Caucasus, the most notorious being the seizure of a school in the town of Beslan, North Ossetia.
The three-day siege of the school, where the attackers held more than 1,000 hostages, ended in a bloodbath, leaving 330 people dead and hundreds wounded.