Suspected New York subway bomber Akayed Ullah has been charged with terror offences, according to police.

Ullah has been charged with making a terroristic threat, supporting an act of terrorism, and criminal possession of a weapon, according to a statement from the New York Police Department.

The state terrorism charges come as federal prosecutors prepare their own case in the rush hour blast in the heart of the city's subway system.

An announcement on federal charges is expected later.

It is unclear if the Bangladeshi immigrant, who is in hospital with burns to his hands and stomach, is well enough to make a court appearance. Only three other people were injured and they suffered ringing in ears and headaches.

Overseas, Bangladesh counterterrorism officers were questioning the wife and other relatives of Ullah, officials there said Tuesday. Relatives and police said Ullah last visited Bangladesh in September to see his wife and newborn son before leaving them behind to return the United States.

Authorities say Ullah intentionally set off the bomb in a long passageway connecting Seventh and Eighth Avenues near Times Square.

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An NYPD official Ullah was not known to authorities before the incident.

Deputy Commissioner for Counterterrorism and Intelligence John Miller said on CBS This Morning that Ullah was not on police or FBI's radar before the Monday morning bomb in Times Square.