Bangladesh on Wednesday launched a hunt for the survivor of a police raid on an extremist hideout which killed nine suspected extremists who claimed to belong to the Islamic State group.

Investigators hope the escaped extremist and another man who was arrested during the major gunfight in Dhaka Tuesday will shed light on the group's proclaimed ties with the IS.

"We've alerted all checkpoints in the capital in a bid to arrest him (the escapee)," deputy commissioner of Dhaka Metropolitan Police, Masud Ahmed, told AFP.

Officers believe the nine slain extremists were part of the same group that killed 22 people during an attack on an upscale Dhaka cafe on July 1 -- an attack claimed by IS.

Police said they recovered IS's black flag and robes from the Dhaka hideout, but maintained that the extremists are actually members of the domestic Islamist group Jamayetul Mujahideen Bangladesh (JMB).

"We're conducting an investigation. Hasan has claimed that they were IS members," a senior security official told AFP, referring to a 25-year-old arrested in the raid who is being treated in hospital

"We suspect he is one of the leading members of the group."

Investigators are also trying to retrieve information from a laptop and several mobile phones recovered in the raid.

IS has claimed responsibility for dozens of murders of religious minority members and foreigners in Bangladesh in recent months.

Bangladesh authorities, however, have steadfastly maintained that the IS has no presence in the world's third-largest Muslim majority nation. They blame homegrown groups such as JMB.

Following the Dhaka cafe attack, IS released photos of five gunmen posing with the group's flag. The group also published gruesome images of the carnage before commandos ended the siege.

Meanwhile, the British Council temporarily closed its offices in Bangladesh Wednesday over safety fears, as a rumor swirled that Islamist extremists would soon target a major market, school or foreign organisation.

"The safety and security of our staff and customers is always our top priority," Barbara Wickham, director of the British Council in Bangladesh, said in a message on its website.

"Therefore we have taken the decision to temporarily close our offices in order to review our security practices."

Many schools and businesses run by the nation's small Christian community closed their doors for days last week fearing an attack from extremists, while several parents have kept their children home from school.