Bangladesh police were scrambling for details about New York subway bomber Akayed Ullah, but uncovered little about the extremist sympathiser. Picture: New York City Taxi and Limousine Commission via AP

Dhaka - Bangladesh police Tuesday were scrambling for details about New York subway bomber Akayed Ullah, but uncovered little about the extremist sympathiser who detonated a homemade pipe bomb in the underground.

The 27-year-old immigrant from Bangladesh set off a crude bomb strapped to his body in a crowded New York subway passage on Monday but the device failed to detonate properly, leaving him the only one seriously harmed.

Ullah told police investigators he wanted to avenge US airstrikes on the Islamic State group and was also inspired by Christmas terror plots in Europe.

Bangladesh police are investigating whether Ullah was radicalised in his Muslim-majority homeland, where foreigners have been among those targeted in deadly assaults claimed by the Islamic State group and al-Qaeda.

Read more: PICS: Four injured as pipe bomb strapped to man explodes in NYC subway

But a probe into his background has revealed little apart from the fact Ullah did not have a criminal record and was not on a watchlist of extremist suspects.

"So far, his name is not on our wide-range list of radicalised persons or members of terror groups, both from Bangladesh and outside," senior counter terrorism police officer Sanwar Hossain told AFP.

"We are trying to gather more details," he said.

Ullah arrived in the United States seven years ago as the member of a family already living there under what is known as "chain immigration".

Also read: Trump slams 'chain migration' after attempted NYC suicide bombing

Bangladesh police said Ullah's family hailed from Sandwip, an island off the coast of the southern port city of Chittagong, but his father had migrated to the capital Dhaka some 30 years ago.

Police could provide little else at this stage about Ullah's early life in Bangladesh.

The impoverished riverine nation of 160 million has been waging a war against homegrown extremism in the wake of numerous attacks by radical groups in recent years.

In July last year militants stormed a Dhaka cafe and massacred 22 hostages, including 18 foreigners, in an assault claimed by the Islamic State group.

Bangladesh last month arrested an alleged militant from Ansarullah Bangla Team, a homegrown extremist group with links to al-Qaeda, over the 2015 stabbing murder of a prominent US blogger in Dhaka.

The secular government of Prime Minister Sheikh Hasina has vowed to root out extremism but says international radical groups do not operate inside Bangladesh. 

Security forces have killed more than 70 alleged militants in a fierce crackdown since the high-profile cafe siege last year.