An explosive device which dropped from the underneath of a police officer's car in Belfast on Sunday was a "viable bomb", Northern Irish police said.

Several homes were evacuated after the discovery of the device in the east of the city, close to police headquarters.

Police Service of Northern Ireland Assistant Chief Constable George Hamilton said: "It is very fortunate that this device was detected before it exploded and that no-one was killed or seriously injured.

"Initial investigations would indicate that this was a viable device placed below an officer's car sometime in the last 48 hours."

Social Democratic and Labour Party lawmaker Conall McDevitt called the attempted bombing "deplorable".

"Those seeking to target police officers are undermining not only the stated will of the people of Ireland who have long since rejected violence, but also the desire for a new beginning for policing in the North, which is shared by the majority of citizens," he said.

"This is a cynical and deplorable act."

British government representative, Northern Ireland Office minister Mike Penning, slammed the attempted attack.

"Those who are responsible offer nothing except terror and misery not just to this police officer and his family but to his neighbours and the wider community," he said.

"Thankfully, due to the vigilance of the officer, no one was injured in this cowardly attack.

"My thoughts are with him and his family at such a distressing time. I also want to pay tribute to the bravery and professionalism of the ATO officers who put their lives on the line by making safe these devices."

Rioting broke out in Belfast earlier this month over a decision by the city's council not to fly the British flag all year round.

Around 3,500 people died in the three decades of violence between Northern Irish Protestants, favouring continued union with Britain, and Catholics seeking a unified Ireland.

A 1998 peace agreement largely ended the conflict, but sporadic unrest and bomb threats continue as dissident offshoots remain violently opposed to the power-sharing government in Belfast, formed of Catholic and Protestant parties.