Two explosions ripped through a district prosecutor's office in the southern Russian province of Dagestan on Friday, touching off a fire and injuring six people.
The attack, the latest act of violence against law enforcement authorities in the unstable republic, occurred at about 9:40 a.m. local time (0540 GMT) in the regional capital, Makhachkala, said Marina Rasulova, a spokeswoman for the city police.
State television pictures showed a towering pall of smoke rising as flames raced through the single-story red brick structure.
"This action was directed against the officers of the prosecutor's office," said Magomed Abdulkhalikov, a deputy prosecutor. "A bomb was thrown from the eighth floor of a newly built nine-story apartment house ... and it exploded just outside the prosecutor's office."
The blast injured four workers at the prosecutor's office and two people passing by, Abdulkhalikov told reporters gathered at the site.
The injured were hospitalized for shrapnel wounds, said Dagestani medical emergencies official Kazanfar Kurbanov.
The cause of the blast is under investigation, Abdulkhalikov said.
"There are several theories," he said in remarks broadcast on the private NTV television channel. "One of them is that it could be people who are being investigated for serious crimes by prosecutors."
It was the third bomb attack on law enforcement authorities in Dagestan in less than a week.
A roadside bomb targeted a police patrol on a main road just outside the provincial capital late Tuesday, killing one officer and wounding two. Just under an hour later, a second less powerful bomb went off in the city, wounding three policemen in another patrol car.
Late last month, attackers targeted another prosecutor's office with a bomb, causing minor damage but no casualties. The explosive device, planted in the basement of a multistory building in Makhachkala, shattered some windows and damaged cars parked nearby, authorities said.
Makhachkala has suffered a spillover of violence from the conflict in Chechnya, but it is also plagued by lawlessness, some of it linked to powerful criminal gangs.
ARSEN MOLLAYEV, Associated Press Writer
Any manifestations of Ukraine's military aggression after the announcement of the results of referendums should be regarded as acts of open aggression against the civilian population of Russia