"It is a well-known fact that the terrorist organisations, backed by the ISI, are actively involved in almost all terrorist activities carried out in the country," BJP President Rajnath Singh told reporters in Hyderabad.

The existence of more than 5,000 sleeper modules operated by ISI is a clear indication that India is virtually sitting on a tinder box, he added.

He alleged that the ISI-sponsored terrorism was thriving in the country due to the UPA government's failure to take stringent action to curb terrorism succumbing to "vote bank politics".

The series of blasts in different parts of the country, including the serial explosions in Jaipur on Tuesday, were the handiwork of ISI-backed terrorist organisations, Singh alleged.

Disagreeing with the argument that Jaipur blasts reflected intelligence failure in BJP-ruled Rajasthan, he said, "Terrorism is not a law and order problem but a national issue. We need a stringent central act on the lines of POTA to deal with terrorist activities."

"The scrapping of POTA without putting in place an alternative anti-terror law had only emboldened terrorists," Singh, who was on his way to Karnataka for election campaign, said.

Quoting US State Department Report on Global terrorism in 2007, the BJP leader said India was among the world's most terror-afflicted countries, accounting for nearly 2,300 of the 22,685 deaths due to terrorism.

Alleging that UPA government at the Centre lacked the will to respond to the challenge effectively, he said there was an urgent need for an integrated plan to launch war against terrorism.

The rapid increase in infiltration into India from neighbouring countries had further aggravated the crisis of internal security, Singh said and sought immediate identification and deportation of infiltrators on a priority basis.