Searches were carried out last night after rioting broke out when the PSNI attempted to speak to the organisers of a suspected illegal Easter Monday pa rade.

Petrol bombs, paint, bottles, stones and other missiles were rained on a police vehicle close to the City Cemetery, where the republican gathering had met.

The trouble broke out at around 3pm and in a police search later in the day, up to 40 petrol bombs were discovered and two youths were arrested.

The police said today that the two teenagers have since been released pending reports.

"Two youths aged 15 and 16 have been arrested by police on suspicion of being in possession of petrol bombs following disorder in Londonderry yesterday afternoon," said a spokesman.

"Shortly before 3pm police in the city were attacked as they attempted to speak to the organisers of what is believed to have been an illegal parade.

"A police vehicle was in the area of the City Cemetery when it came under a sustained attack by a crowd throwing containers of paint, petrol bombs, stones, bottles and other missiles.

"During the disorder a crowd of up to 70 people attacked police vehicles and set fire to traffic signs in the area. Police recovered over 40 petrol bombs and enquiries into the incident are ongoing."

Yesterday's unrest flared three days after police investigating a sudden death in Creggan were pelted with petrol bombs and paint in Iniscarn Road.

Creggan SDLP councillor, Jim Clifford, said he saw between 50 to 60 youths gathered close to the cemetery at one stage and warned against "recreational rioting".

"It has got to the stage where the young ones know the police are going to be there at these parades and they are just waiting for what people call recreational rioting," he said.

"What these young people don't realise is that someone is going to be killed. One of these petrol bombs is going to hit a house or a passing car or catch someone, or the petrol could spill and they could end up setting themselves on fire, it's not the first time that ever happened."

He added: "Parents need to catch themselves on and stop their sons and daughters getting caught up in this sort of thing.

"Younger ones just copy the teenagers and they get dragged into it too."