The head of a Bangladeshi Islamist group accused of carrying out a deadly siege at a cafe in July died during an arrest operation earlier this month, an elite security unit said Friday.



Abdur Rahman died in hospital on October 8 after jumping from the fifth floor of a building on the outskirts of Dhaka while attempting to evade arrest, the Rapid Action Battalion (RAB) said in a statement.



The identity of Rahman, who was leader of the Jamayetul Mujahideen Bangladesh (JMB), was later confirmed through his possessions and by his family who were shown pictures of his body, the statement added.



Several documents, letters and emails that were later retrieved by the RAB "all proved that Abdur Rahman was the emir (head) of the new JMB".



Bangladeshi authorities are insistent that the JMB was behind a siege at an upmarket cafe in Dhaka on July 1 in which 20 mostly foreign hostages were killed, even though the Islamic State group claimed responsibility.



At least 40 JMB followers have been killed in a crackdown against the group since the attack and dozens of raids have been carried out at addresses linked to the outfit.



The JMB, long dormant after their top leaders were executed in March 2007, is believed to have recently regrouped with young and university-educated extremists taking the helm.



Bangladesh has been reeling from a wave of recent attacks with targets including foreigners, rights activists and members of religious minorities.



Critics say Prime Minister Sheikh Hasina's administration is in denial about the nature of the threat posed by Islamist extremists. They accuse her of trying to exploit the attacks to demonise her domestic opponents.



In August US Secretary of State John Kerry said during a visit to Dhaka that evidence existed to link the extremists behind the attacks in Bangladesh to IS.