Army bomb disposal robots are seen next to a suspected vehicle as a controlled explosion takes place at the scene of a security alert in Londonderry, Northern Ireland, January 21, 2019. REUTERS/Clodagh Kilcoyne

LONDONDERRY, Northern Ireland (Reuters) - There was a large bang and black smoke emerged from an abandoned van in a cordoned off area of Londonderry on Monday after an army bomb disposal robot entered the vehicle, a Reuters witness said on Monday.

A police officer at the scene told the witness that the army was preparing to conduct a controlled explosion on the vehicle that was hijacked by three masked men who threw an object in the back before abandoning it.

There was a second loud bang at the same vehicle minutes later, the witness said.