Three people have been arrested after police discovered four mortar bombs in a van in Londonderry. The arms cache was believed to be in preparation for an attack on a police station, detectives said.

About 100 homes in the Letterkenny Road area of Derry were cleared as police taped off the area around the vehicle.

Two men aged 37 and 35 were arrested at the scene. A third man, aged 37, was arrested at another address.

Police say the van had its roof cut back in order to allow the mortars to be fired from it. Officers believe the intended target was a nearby police station and linked the attack to dissident Republicans.

Pat Ramsay, an SDLP member of the Northern Ireland Assembly, who attended the scene of the security alert, said petrol bombs were thrown at police who were helping people evacuate their homes.

He said: "This discovery of a possible viable device by PSNI reminds us of those who would recklessly endanger the lives of people in this community.

"I cannot state it any stronger: I want to make it clear that the people of Derry do not want this and those behind it need to stop.

"I am calling on anyone with information to come forward and assist police with their ongoing investigations in regards to recent attacks on our community."

Ramsey said those responsible were "bringing nothing but distress and disruption to the people of this city".

"I was appalled when I saw a petrol bomb getting thrown at a police car. No-one was injured but it was very upsetting."

Bomb disposal officers were also called to an area in south Belfast after a suspicious object was found. A controlled explosion was carried out. The package was later deemed to be a hoax.

In February, police seized a rocket launcher and a warhead in raids on a house in west Belfast during investigations into dissident Republican activity.