Home Minister Shivraj Patil on Monday informed the Lok Sabha that the serial bomb blasts in three cities of Uttar Pradesh on Friday were triggered by battery-operated timer devices.

In a statement during the Zero Hour, he said explosives with the timers were contained in bags kept on bicycles parked close to areas, where lawyers and litigants relax on court premises, the scene of explosions.

He said teams of the National Security Guards had visited the blast sites for post-blast investigations. However, the probe into the multiple blasts is being carried out by the Special Task Force (STF) of the Uttar Pradesh police with the assistance from Central agencies, he added.

The home minister said as per the latest information, five bomb blasts happened in three cities of Varanasi, Faizabad and Lucknow in 20 minutes.

He said Minister of State for Home Sriprakash Jaiswal, along with officials of the ministry, visited the blast sites in Varanasi.

Condemning the mindless terrorist violence, Patil reiterated government's firm resolve to combat terrorism, adding fight against it had to be fought by the government, political parties, civil society and the media together.

"'We will not allow these anti-national forces to disturb peace and communal harmony in the country."