The Officer-in-Charge of Rupsha thana received a letter on Thursday that threatened to blow up the police station.

Though the sender did not identify himself, the letter threatening to blow up Rupsha thana was sent by JMB to retaliate arrest of trained JMB activist Shahidullah alias Lokman, the SP told newsmen Friday night.

Shahidullah, a student of Bamondanga Madrasa in Khulna, was arrested in Dhaka on September 8 in the case filed in connection with bomb blasts on Khulna court compound earlier.

Security has been tightened in and around all police stations in Khulna after the threat.

The Rupsha thana OC had earlier said that the letter might have been sent by an Islamist militant organisation.

The letter said Rupsha police station was on the list of police stations across the country that will be targeted for attack to avenge the arrest of Islamist militants.

It said JMB activists are being arrested across the country. Shahidulla has been arrested in Khulna. If he is not released, JMB will blow up Rupsha thana as part of a plan to attack "all police stations and key installations" in the country, it said.

Shahidullah was brought to Khulna for interrogation and is now in Khulna jail. He may be produced before court today for further remand, police sources told this correspondent yesterday.

They said that during interrogation Shahidulla said he was trained in making and using bombs and grenades and use of firearms.

He also told interrogators that JMB chief Abdur Rahman used to visit Bamondanga Madrasa every three months to know about training of Islamist militants in the institution.

OC Mizanur Rahman said the sender did not mention his organisational affiliation in the letter.

Earlier on Tuesday, a man identifying himself as Siddiqul Islam Bangla Bhai of outlawed Jagrata Muslim Janata Bangladesh (JMJB), demanded toll from the Commissioner of Benapole land customs over cell phone.

Customs Commissioner Hussein Ahmed confirmed the incident on Thursday night and said the unidentified caller demanded a big amount of money from him for treatment of many militants who were injured in different incidents.

The caller threatened the customs commissioner with "dire consequences" if he does not send the money.

"I was asked by the caller to call a cell phone (no 0175-362132) for giving information on whether the money was sent," the commissioner said.

"Bangla Bhai does not go to any one for money, rather you are to go to him with money to save your life," the caller said when the customs commissioner asked him to come to his Benapole office to talk about the matter.

Security measures have been tightened at Benapole land customs office following the incident.