Army technical officers carry out controlled explosion on Craigavon Bridge
A controlled explosion has been carried out on a suspicious object on the Craigavon Bridge in Londonderry.
Army technical officers carried out the explosion shortly before 1700 BST.
Acting Chief Inspector Jon Burrows, the Foyle area commander, has condemned those responsible for placing the device.
He said whether the device was real or a hoax the act was "callous and reckless in the extreme".
The device is believed to be on the lower deck, but both decks of the bridge have been closed while police examine the scene.
The acting chief inspector called the perpetrators "selfish cowards" and said they "don't give a damn about the people of this city".
"There is understandable dismay and anger in the city over the inconvenience caused by this alert."
He said that someone needing emergency medical treatment on the cityside "could be put at additional risk because of the delays of either getting to hospital via the new bridge, or delays in medical assistance reaching them".
The incident has caused massive disruption to traffic in the city. Motorists have been warned to expect delays of an hour or more.
The police are not yet able to estimate when the bridge will reopen.
The bridge was also the subject of a security alert on Tuesday. Nothing was found when the area was searched.