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Police in Londonderry say Radio 1's Big Weekend is their biggest security operation of the year.

Chief Inspector Tony Callaghan from the Police Service of Northern Ireland (PSNI) has overseen the planning of the event.

He says he will have enough police deployed on the ground to curb any anti-social behaviour.

"City life has to go on as normal," he said. "The police are here to support the event."

Forty-thousand people are due to attend the three-day event being held in Derry's Ebrington Square.

The ongoing threat from dissidents in Derry and throughout Northern Ireland is labelled "severe" by the security services.

In March, a van loaded with mortar bombs was intercepted in the city with the target believed to have been a police station.

Guns, ammunition and a suspected pipe bomb were found in April when two cars were stopped in Derry.

However, Chief Inspector Callaghan said Big Weekend was a very different situation.

"The planning has been in the making for six to nine months now," he said.

"Clearly there is no 100% guarantee with these things but I'm confident we can deal with most eventualities."

He wouldn't confirm how many police would be deployed at the event but said it was enough "to deal with whatever's thrown at us".

Chief Inspector Callaghan also issued a warning to people intending to cause trouble.

"We have stewarding in abundance, we have police in abundance," he said. "You will be arrested and prosecuted if you're involved in any criminality."

Calvin Harris, Biffy Clyro and Bruno Mars are headlining Big Weekend.

Other acts performing across the weekend include Olly Murs, The Vaccines and Foals.

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