Moscow: Four persons were killed and many more casualties feared in a powerful bomb blast outside the regional headquarters of Russia's Security Services in Ingushetia bordering Chechnya.

Authorities confirmed four deaths and feared a large number of casualties, as about 100 people were inside the Federal Security Services office at the time of blast at 11.55 am (1.25 pm IST), the ITAR- TASS agency said, adding the building suffered serious damage in the blast.

Chechen rebels are believed to be behind the attack, though no one has claimed responsibility till now.

PTI