President Alexander Lukashenko said that a blast that tore through a crowded metro station in the Belarus capital Minsk in evening rush hour killing 11 people was an attempt to destabilize the country.
As police placed the capital on high alert, Lukashenko, who has led the ex-Soviet country since 1994, linked the explosion to a previous unsolved blast in 2008, saying: "These are perhaps links in a single chain."
Acts of deliberate violence are unusual in Belarus, a republic of 10 million people which shares borders with EU members Poland, Latvia and Lithuania and with Russia and Ukraine.
"We must find out who gained by undermining peace and stability in the country, who stands behind this," said the president.
One opposition figure said he feared Lukashenko would use the blast to crack down even more harshly on political rivals.
"Prosecutors qualify this as a terrorist act," a source in Lukashenko's administration told Reuters.
Lukashenko, who is at odds with Western governments over a police crackdown on an opposition rally against his re-election last December, said: "I do not rule out that this (the blast) was a gift from abroad."
Monday's blast occurred on a platform at around 6 p.m. at the Oktyabrskaya metro station -- one of the city's busiest underground rail junctions -- about 100 m (yards) from the main presidential headquarters.
Lukashenko was quoted by Interfax news agency as saying 11 people had been killed and 100 injured. A presidential administration source later said 126 people had been injured.
In his remarks, Lukashenko referred back to July 2008 when a home-made bomb wounded about 50 people at an open air concert he was attending. The crime was never solved.