Cops of the Special Task Force (STF) on Tuesday evening seized four truckloads of illegal firecrackers from two different points in North 24-Parganas, two days after the Duttapukur blast in the district which claimed at least nine lives.

The haul raised questions about how the large-scale production of illegal firecrackers could not be prevented by police even after directives to crack down on such units after the explosion in East Midnapore's Egra on May 16 this year that killed 12 persons.

An STF officer said that although the amount of firecrackers had not been measured so far, each truck was loaded with at least 10 tonnes of banned crackers. The STF has also detained two persons for their suspected connection with the firecrackers.

A source said the trucks were loaded from illegal factories in Duttapukur after Sunday's explosion and were kept in two strategic locations of North 24-Parganas to avoid detection.

"According to information, all four trucks were loaded from a storehouse in the Duttapukur after the explosion and kept in two strategic locations. There was a plan to send those fireworks to their strategic hideouts. We have informed the bomb disposal squad for further steps," said a senior officer in the STF.

Nine persons were killed so far in an explosion in an illegal fireworks unit at Mojpole-Paschimpara village of Duttapukur on Sunday.

A source in the STF said two trucks were seized from a parking lot in Boardghar under the New Barrackpore police station area, while the remaining two were seized from Beraberia under the Amdanga police station area.

After Tuesday's seizure of firecrackers, a section of senior police officers pointed out how the large-scale production of illegal explosives was in operation even after the state police had issued several guidelines to prevent the practice.

"The seizure of huge firecrackers from two different locations proved that racket of illegal operation was very much active even after recent large-scale explosions. After the Egra blast, all police officers were asked to close down all such units as soon as possible. Sunday's explosion proved there was no vigilance by police in the region at all," said a senior police officer.

Chief minister Mamata Banerjee had expressed her embarrassment at police inaction in her cabinet meeting on Monday and asked top police officers to crack down on those units as soon as possible.

The inspector-in-charge of Duttapukur police station and another police officer were suspended on Monday within hours of the chief minister questioning police inaction.

A source said after Mamata raised questions on police vigil, the home department has asked all district police chiefs to trace illegal fireworks units and explosive storehouses in their respective areas.