Some of the 300 suspects arrested in connection with the explosions have confessed to having links to the attacks. But they barely can name the leaders of their immediate upper tier, leave alone the masterminds, sources in the intelligence agencies said.

"We need to arrest the leaders of the next tier for further developments. But it seems very tough as the arrestees can hardly identify their immediate senior leaders," said an investigator asking not to be named.

Those who have admitted to having links to the blasts, which killed three people and wounded over 100, are members of the banned Jama'atul Mujahideen Bangladesh (JMB) and Jagrata Muslim Janata, Bangladesh (JMJB). According to the confessions, they carried out the attacks at the call of JMB chief Abdur Rahman.

The home ministry at a recent meeting has discussed intelligence agency reports that said JMB and outlawed Janajuddha were involved in the blasts.

Sources said if Janajuddha was involved, its second-in-command Saifuzzaman alias Shoaib alias Ripon, who died in Rab action on Monday, could have given important clues.

Besides, there are allegations a large number of Jamaat-e-Islami and its student wing Islami Chhatra Shibir activists, who were arrested in connection with the blasts, were released without keeping records of their arrest.

Initially, law enforcers were carrying out combing operations across the country to net the suspects. But now they look very reluctant despite reports that the JMB and the JMJB are recruiting members to form suicide squads.

The Islamist extremists are also continuing their activities in the remote char areas in different northern districts, but the law enforcers are not raiding these areas.

An intelligence agency official in Rangpur has recently told The Daily Star now the drive against the militants are totally controlled by the top officials in Dhaka.

The arrestees are field level JMB activists or cadres who were only assigned to plant bombs and blast those at the directives of their immediate bosses, another intelligence agency man said.

The cadres or field level activists only know their immediate bosses as "responsible persons", the official said asking not to be named.

If a field level activist dares to learn the identities of his upper level bosses, he is subject to severe punishment and torture like gauging out of eyes, the official said quoting a detained JMB activist.

Meanwhile, Ishraq Ahmed Siraji, a close associate of detained Farid Uddin Masud, was taken on a five-day fresh remand yesterday.

Siraji was produced before the Court of Chief Metropolitan Magistrate, Dhaka with a seven-day remand petition on completion of his five-day remand.

In the forwarding placed before the court, the investigation officer (IO) of the case said Siraji gave important information about withdrawal of huge amount of money from his bank accounts that was spent to carry out the blasts.

Our staff correspondent from Khulna reports: Police recovered two powerful bombs from in front of "Beg Manjil" at Mianpara in the city yesterday.

Police also seized a letter written by Akram Hossain Khokon in the name of Harkat-ul-Jihad.

Introducing himself as a commander of the outfit, Akram asked 'his' cadres to implement the mission to kill Khulna City Mayor Shaikh Tayebur Rahman and city BNP Secretary Nazrul Islam Manju.

"Money is no problem," Akram wrote in the letter.

Meanwhile, Dr Masud Bin Ishaque, arrested in Khalishpur in the city on Monday, was taken on a 12-day remand and later sent to the Joint Interrogation Cell (JIC) in Dhaka.

He introduced himself as a leader of Jama'atul Muslemin, a militant outfit.

In another development, police arrested JMB activist Daud Shaikh from Udaypur village under Mollahat upazila of Bagerhat on Tuesday and seized 20 booklets and 19 leaflets of the outfit.

Police said Daud is a member of the 'JMB suicide squad'.

Our staff correspondent from Chittagong adds: Investigators of JIC in Chittagong yesterday took five suspects on a seven-day fresh remand.

They were produced before a court with a prayer for eight-day remand on completion of their earlier seven-day remand.

The five are Ahle Hadith chief Asadullah Galib's nephew Sadrul Alam, Arshadul Alam, Jahangir Alam, Abdus Satter Mollah and Ahmed Mia.