Russian security officers work at the scene of an explosion in Moscow March 9, 2011. A blast tore through a bus stop on Wednesday near Moscow's training centre for the federal security services, injuring no one, police and the national anti-terror committee said.[Photo/Agencies]

MOSCOW -- A blast tore through a bus stop on Wednesday near Moscow's training centre for the federal security services, injuring no one, police and the national anti-terror committee said.

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"An unidentified explosive device blew up at a bus station at about 4.30 pm (1330 GMT)," said spokesman Nikolai Sintsov, from the national anti-terror committee.

A police spokesman confirmed there were no casualties from the explosion near the FSB Academy, which trains future security officers. The explosion comes on the first day of a visit by US Vice President Joe Biden.A decade after federal forces drove separatists out of power in a second war in Chechnya, analysts say the Kremlin is waging a losing battle with militants in its mainly Muslim North Caucasus region, who want to carve out a separate Islamic state.

Last week the rebels' Chechen-born leader Doku Umarov threatened in a video address more attacks on major targets across Russia, six weeks after a suicide bomber killed 37 people at Russia's busiest airport.

Interfax news agency quoted the national anti-terror committee as saying there was some damage to cars near the bus stop on Wednesday.