The Real IRA is believed to be responsible for an explosion at a Royal Mail sorting office in north west London last night.
The head of Scotland Yard's anti-terrorist branch, Deputy Assistant Commissioner Alan Fry said the blast in Hendon was caused by a high explosive device.
Speaking at the scene, he commented: "A high explosive device was placed outside the sorting office in a bricked-up former doorway. It exploded at 11.28 p.m.
"We believe it contained between half and one pound of high explosives, which was a similar size to the device at Hammersmith Bridge in June last year.
"Minor damage was caused to the building. No threats were made. We suspect it was the work of the Real IRA."
Mr Fry said although no one was in the delivery depot, the building was near a pub and the busy Edgware Road.
He added: "Whoever planted this device had no thought to the damage or injuries he may have caused."
A spokesman for Consignia, the Royal Mail's new corporate name, said the building was a small delivery office which deals with mail for the NW9 area. It was one of 100 similarly-sized buildings in the capital.
He added that no-one was working in the building at the time.
PA