The FBI is seeking two men who were allegedly seen removing a bomb from a suitcase in New York - in the same hour that another explosive device detonated just a few blocks away.

The men - who are being sought as witnesses not suspects - appeared to take the suitcase, leaving the bomb behind.

The development comes just hours after federal prosecutors charged Ahmad Khan Rahami, the main suspect in the New York-New Jersey weekend bombings, with using a weapon of mass destruction.

Rahami, 28, is accused of planting the bombs, including one which injured 31 people when it blew up on a bustling Manhattan street.

The bomb that had been in the suitcase did not explode.

FBI seeks public's help in locating two men related to NY/NJ investigation https://t.co/tOaCR7Ujay pic.twitter.com/2yXfCfLGWH

— FBI (@FBI) September 21, 2016

Rahami, who was born in Afghanistan, was captured on Monday after he was wounded in a gunfight in Linden, New Jersey.

He also faces five counts of attempted murder in connection with that shootout.

Although federal agents have tried to question him, US officials say he has not been co-operating.

The image of the two unidentified men is taken from CCTV recordings between 8pm and 9pm on West 27th Street between 6th and 7th Avenues on Saturday, September 17th, the FBI said.

The FBI has said the suitcase could be a "really rich environment" for evidence and a "key part" of the investigation, she said.