Kolkata, Jan 28 (IANS): The Indian government's failure to develop a better understanding of the 26/11 Mumbai terror attack and learn crucial lessons was "tremendously worrying", said an author here.

Adrian Levy, co-author of "The Siege: Three Days of Terror Inside the Taj", said New Delhi should look into the complexities of the incidents.

The book provides a detailed insight into the Mumbai terror attack.

"What they need is more knowledge... not less... greater understanding of the series of events and look into the complexities of the attack," Levy said during a session at the third Kolkata Literary Meet here Monday.

The author said the Indian intelligence agencies had received 26 alerts from the CIA before the terrorist strike on India's commercial capital by 10 Pakistani gunmen Nov 26, 2008.

The alerts forewarned of a fidayeen attack, involving a dozen gunmen making a sea landing in Mumbai and even about most of the targets of the three-day assault that left 166 people, including foreigners, dead.

The book, co-authored by Cathy Scott-Clark, claims a Major Iqbal of Pakistan's Inter-Services Intelligence (ISI) boasted of a super agent dubbed "Honey Bee" in New Delhi, who passed them classified files on the training manuals of the Indian police and army commandos.

"The National Security Guards did a remarkable job... the fact they were late had nothing to do with them... they were let down from the bureaucracy side," Levy said.

Commenting on the National Security Agency's (NSA) controversial surveillance practices, revealed by Edward Snowden, a former US defence contractor, Levy said "more intrusion" was not the answer to security.

"It's a tremendously claustrophobic experience to think that everything we have from Gmail, to research, to media, is being actively observed in real-time... I don't think more intrusion is the answer at all... I think greater understanding and political solutions are needed."