DHAKA - A US national of Bangladesh origin was among nine suspected Islamist extremists killed in a massive gunfight in Dhaka, police said Wednesday.

Dhaka Metropolitan Police spokesman Masudur Rahman told AFP that Shahzad Rouf was one of nine young men who were killed during Tuesday's early morning raid on a militant hideout.

"He was an American citizen. We confirmed his identity by checking finger prints," he told AFP. He said six other extremists were also identified by police investigators by matching their finger prints with their national identity cards.

The nine were shot dead when hundreds of armed police stormed their den at a six-storey apartment building in Dhaka's Kalyanpur neighbourhood.

Police on Wednesday launched a hunt for a survivor of the raid. Investigators hope the escaped extremist and another man who was arrested during the gunfight will shed light on the group's claimed ties with the Islamic State group (IS).

Rouf, 24, was a business administration student at the North South University (NSU), Rahman said.

Local media said he was a close friend of Nibras Islam, one of five gunmen who attacked an upscale Dhaka cafe on July 1 and killed 22 people, mostly foreigners.

Police believe the nine were part of the same group that carried out the cafe attack.

NSU, a top private university where well-off people send their children for higher education, has been a hotbed of Islamist extremism.

Another of its students was shot dead in a northern Bangladesh town a week after the Dhaka cafe attack when Islamists launched a major assault on the country's largest Eid prayer congregation, where some 250,000 people gathered.

Seven of its students were also convicted and jailed in December last year for the murder of an atheist blogger in early 2013, kickstarting a deadly campaign against secular activists and religious minorities.

Dhaka police chief Asaduzzaman Mia told reporters after the raid that most of the extremists killed in the operation were highly educated and from the country's elite.

- Islamic State? -

Rouf's father, Touhid Rouf, told AFP that he was shown a body, but was not sure whether it was that of his son.

"I am not 100 percent sure. I am confused. Maybe it is because the body had an autopsy and it was partly decomposed. We need a DNA test," he told AFP.

He confirmed that his son was an American passport holder and that he had been missing from home for the last six months.

A US embassy spokesman refused to comment on Rouf's case.

Rouf had been named on a list of missing people prepared by the elite security force Rapid Action Battalion after authorities raised concerns that he might have fled the country and joined the Islamic State group.

The nine had claimed that they were members of the Islamic State organisation, with officers recovering the group's black flags and robes from their hideout.

But the national police chief rejected the claim, asserting that the nine were members of banned homegrown militant outfit Jamayetul Mujahideen Bangladesh (JMB).

IS said it was responsible for the attack, releasing images of the carnage and photos of the five gunmen posing with the group's flag.The group 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.

The government of Prime Minister Sheikh Hasina has launched a nationwide man-hunt for Islamists, arresting more than a dozen suspected extremists including one of JMB's regional heads.