Alert was cleared after a passenger onboard the Delta/Northwest Airlines Flight 253, where a Nigerian attempted to set off an explosive device on the Christmas Day, was reported to be "verbally disruptive" on Sunday when the airplane was landing, said officials.

Security officials at the Detroit Metro Airport "responded to a report from an incoming flight from Amsterdam where a passenger spent a lengthy time in the restroom. This raised concerns so an alert was raised," said the Federal Bureau of Investigation (FBI) in a statement.

The FBI said that the incident was a "non-serious incident," and cleared the alert it triggered.

The Delta Air, who owns the Northwest Airlines, confirmed that a Nigerian man had locked himself in the airplane's lavatory for one hour and became verbally disruptive.

In response to the incident, crew members had to requested emergency assistance upon arrival, asking for security personnel to remove the man from the airplane after it landed, said a spokeswoman from the airlines.

All other 255 passengers got off safely, she added.

Seen from footages of U.S. local TV channels, emergency units including firefighters were deployed around the airplane that was held at a remote location, and all luggage were lined up on the ground for further check.

The U.S. authorities said that this is a separate incident from the Christmas Day terror attack attempt, and no device was found on or with the passenger in this latest incident.

U.S. President Barack Obama, who is on his vocation in Hawaii, has been notified the latest development of the incident, and stressed importance of maintaining "heightened security measures."

Two days earlier, another Nigerian, identified as Umar Farouk Abdulmutallab, attempted to set off an explosive device on the Delta/Northwest Flight 253, which flies from Amsterdam, the Netherlands, to Detroit, Michigan.

The failed bombing attack has triggered a stricter security screening for travelers entering the United States and investigation in the terrorist watch list by U.S. authorities.