Police said the security alert in the Maureen Avenue area, which began on Monday and lasted overnight, has now ended.

Several suspicious items were found at a property and made safe by the army bomb squad, who have now removed them for further testing.

Chief Inspector Garry Eaton said: "These viable devices were found in a flat, in the middle of a built up residential area which could have caused significant damage or serious harm to local people.

"Evacuating the area caused disruption but our primary concern is to keep people safe and prevent injury to the public."

The Foyle Area Commander continued: "The very nature of those devices is that they are unpredictable.

"I'm not going to speculate as to where they were ultimately intended for but the fact that they were in residential premises means they presented a real and serious risk to people.

"We're lucky we're not dealing this morning with serious injury or death."

Residents evacuated from their homes were allowed to return to their properties by Tuesday evening.

A 30-year-old man was arrested on suspicion of dissident republican activity during the alert.

He is being held in custody helping police with their enquiries.

A local councillor has condemned the discovery.

The SDLP's John Boyle said: "I am deeply shocked that police have discovered a number of devices that were capable of causing serious harm."

"It is especially alarming that these devices were left in an apartment in a built-up area as that could have concentrated the damage caused had they exploded.

"There is no support in Derry for acts such as this and creating a culture of fear in the town cannot further any cause by so much as an inch.

"Those behind these devices are enemies of the community - they must be found and face the criminal justice system."

Anyone with further information has been asked to come forward to the police.