Moscow: Twin blasts rocked northern Moscow on Friday in an attack that left no casualties but appeared part of a campaign against targets linked to the powerful Federal Security Service (FSB).
The two bombs -- one left on top of an outdoor garage and the other left in a metal garbage container -- went off outside a building housing FSB employees and their families, police sources told Russian news agencies.
"The blasts went off one after the other," Interfax quoted a police spokesman as saying. "Each bomb had the blast equivalent of about 150 grammes of TNT."
Nails packed with the explosives shattered glass across seven floors of the high-rise building, with the head of the Moscow FSB`s investigative unit heading out to the site to personally inspect the damage, RIA Novosti reported.
"We have double-pane insulated windows, but even these were shattered by the nails," the lifenews.ru quoted one local resident as saying. "I looked outside, and then the second bomb went off before my very eyes."
Police sources said the explosives were similar to the small bomb that went off on Wednesday outside a bus stop near an FSB training centre in Moscow.
"We are working on several versions of events, but our experts do not rule out the links between these two explosions," a police source told Interax.
Wednesday`s blast has been claimed by the Riyadus Salikhin Martyrs Brigade, an Islamist group founded by the Chechen warlord Shamil Basayev before his violent death in 2006.
The groups said in a statement posted on the Kavkazcenter.com website popular with Islamists that Wednesday`s attack was carried out in reprisal for past FSB operations in the Caucasus.
"We intend to continue striking facilities and places where the (FSB) criminals gather," the statement said.
The explosions followed a massive January 24 blast that killed 37 people and wounded more than 100 in Moscow`s busiest airport Domodedovo.
After a lull of several years, suicide attacks returned to Russia last March when two female suicide bombers from the Caucasus killed 40 and wounded dozens on the Moscow underground.
One of those two underground blasts occurred near the FSB headquarters in central Moscow.
Russia`s leading Islamist rebel Doku Umarov has claimed both attacks and vowed to make 2011 "a year of blood and tears”.
Police officials however labelled Wednesday`s attack "an act of hooliganism" and appeared determined not launch a terror probe following Friday`s explosions.
"Since there are no casualties, this incident will probably be qualified as a hooligan prank," another police source told Interfax.