The van was abandoned on a bridge in the village of Clady
A controlled explosion has been carried out on a van in the County Tyrone village of Clady, after police were told a 600lb bomb had been left in it.
The vehicle was abandoned on a bridge in the village on Wednesday night with its hazard warning lights on. Two men, aged 34 and 28, have been arrested.
A number of roads to the village have been closed as the alert continues. Army bomb experts are at the scene.
Meanwhile, another alert in Limavady has ended.
An object found outside a house at Meadowvale Park turned out to be innocuous.
Police received the warning about the Clady bomb by telephone. Locals noticed a van parked on the Urney Road Bridge at about 2100 BST.
Independent councillor Gerard Foley was one of the first to come across the van.
"We stood and looked at it for about 10 or 15 minutes and we said, 'there's something not right here'," he said.
"So we cordoned off the street and put cones across the road, and then we phoned the police.
"There is no support in this community for what is happening, (people) don't want this in Clady at all."
Roads in the Irish Republic leading to Clady have also been closed
Ulster Unionist councillor Derek Hussey said he "unreservedly condemned" the disruption caused by the incident.
"The closure of a cross-border road has caused a great deal of traffic disruption.
"An incident such as this only serves to heighten concerns within the community, particularly in the context of the recent dissident activity across the province," he said.
West Tyrone MP Pat Doherty said that 14 hours had now passed since the police first received the warning.
"Obviously I would like to see this situation cleared up as quickly as possible.
"The residents don't know what's going on, and they're apprehensive.
"They need to be kept informed as to what's going to happen here.
"Whoever parked the van there or planted the device, if there is a device, really needs to catch themselves on.
"It's a disgrace," he said.