Bangladeshi forces Saturday killed eleven suspected Islamist extremists including the new leader of a banned group behind a massacre at a Dhaka cafe this year, a minister said.

"Eleven extremists were killed. They are all members of the new JMB (Jamayetul Mujahideen Bangladesh)," Home minister Asaduzzaman Khan told AFP, referring to the outlawed group that killed 22 mostly foreign hostages at the cafe in July.

"The dead included Akash who was leading the new JMB after the death of Tamim Chowdhury," he said, adding seven of the extremists were killed in a gunfight in Patertek, Gazipur district, just outside Dhaka, after they rejected an offer to surrender.

Chowdhury, a Canadian citizen of Bangladesh origin, was shot dead in a gunfight last month. Police said he was the leader of the JMB and was the mastermind behind the cafe attack.

The minister said seven more suspected Islamist extremists were also arrested in raids in two industrial towns just outside the capital after they committed robberies to fund their activities.

"We have seized money from these extremists that they got through robbery," he said.

Police said Akash could be a code name for the slain JMB leader.

Earlier in the day the elite Rapid Action Battalion launched two separate operations after being tipped off about the presence of Islamist extremists in a building in Gazipur, just outside Dhaka, and a three-storey structure in the northern district of Tangail.

"Four extremists were shot dead during a gunfight with the RAB in the two places. They are new JMB members," RAB spokesman Mufti Mahmud Khan told AFP.

The Islamic State group claimed responsibility for the July 1 attack on the upscale cafe in Dhaka, posting pictures of the attackers holding IS flags online.

However, Bangladesh officials have rejected the claims, saying the JMB was responsible for the massacre.

In August police shot dead 30-year-old Chowdhury dead along with two of his associates after they stormed an extremist hideout in Narayanganj city near Dhaka.

Long dormant after their top leaders were executed in March 2007, the JMB has recently regrouped with young, university-educated extremists taking the helm.

Bangladesh has been reeling from a deadly wave of attacks in the last three years, including on foreigners, rights activists and members of the country's religious minorities.