Beirut - A hand grenade went off Thursday morning in Beirut's Sunni district of Nuwairi, causing panic but no casualties, police said.

Police said the blast took place in an abandoned two-story building in the neighborhood where the majority are followers of the late former Prime Minister Rafik Hariri, who was assassinated on February 14, 2005.

Lebanese army troops and police swiftly cordoned off the area and opened an investigation into the incident.

According to Lebanese security sources the grenade was believed to have been meant to scare people away from participating in the planned mass demonstration in Beirut's downtown district to marke the the fourth anniversary of Hariri's killing in a bomb attack.

Hariri's anti-Syrian Future Current Movement is still at odds with the Hezbollah-led opposition in Lebanon. (dpa)