Dissident republicans are likely to launch a terrorist attack during next month's G8 leaders' summit in Northern Ireland, police have warned.

With world leaders including Barack Obama and Vladimir Putin in attendance, the summit, at the Lough Erne golf resort in Fermanagh on 17 and 18 June, has prompted the biggest police operation in Northern Ireland's history, involving 8,000 officers, 4,400 of them local and 3,600 from England and Wales.

Alistair Finlay, the assistant chief constable of the Police Service of Northern Ireland (PSNI), said: "During the G8 is a great opportunity for those groups … threatening harm to communities and threatening harm to my officers. People should not be surprised if there are incidents."

With the enlarged police presence surrounding the summit, Finlay said the threat was more likely to manifest itself elsewhere, in areas such as north and west Belfast, Newry and Derry. "What we anticipate is those incidents wouldn't be at, near or affecting any element of the G8," he said.

He said the threat was not necessarily directly linked to the summit but a consequence of the normal "rhythm of life" in the province. Groups such as the New IRA and Óglaigh na hÉireann continue to carry out attacks in Northern Ireland, and have more sophisticated weapons than dissidents have had for some years.

Finlay said he was "very aware" that terrorists carried out the 7 July attacks on London during the last G8 summit held in the UK, which was in Gleneagles, in Scotland, in 2005. Despite the threat, he described the Fermanagh summit as a "great opportunity" for the province to promote itself.

As well as preventing terrorist attacks, the police operation is charged with controlling protests. The PSNI has armoured cars and a water cannon at its disposal. Reports have suggested that Metropolitan police officers are being trained in the use of water cannon, but Finlay said they were being trained only in how to react if they are on the streets when it is deployed; they would not be operating the cannon themselves.

He said the police were committed to "facilitative, community-based policing", and would resort to robust tactics only in the event of any threat.

Protests are planned in Belfast before the summit, on the weekend of 15 and 16 June, and a demonstration that organisers hope will attract 20,000 people is scheduled for the first day of the summit in Eniskillen, close to where the world leaders are meeting.

Finlay said there was no indication that significant numbers of people intent on causing violence during the protests were travelling to the summit, and he was expecting fewer people than at Gleneagles.

He put this down partly to the remoteness of the location and also to the fact that demonstrations were being held in Dublin and London.

Groups planning to demonstrate include anti-capitalists, anti-fracking groups and unionists protesting against the decision to limit the number of days the union flag flies over Belfast City Hall.

With the G8 summit only 15 miles from the border with the Republic of Ireland, the PSNI has been closely co-operating with the gardai. The republic's justice minister, Alan Shatter, is bringing in legislation before the summit allowing gardai to order telecoms companies to shut off signals in order to stop terrorists using mobile phones to detonate bombs.