Sir Ronnie Flanagan said those responsible for throwing a grenade at a pub in Co Londonderry on Monday, and other attacks in recent weeks were deliberately targeting the Good Friday agreement.

"I think continuing attacks by loyalists are designed specifically to unnerve others, to bring about a reaction and to attack the peace process," he said.

"Everybody must be alive to that threat and do everything they can to thwart it."

Several people escaped injury when there was a small explosion outside McNally's pub in Castledawson on Monday night. The loyalist splinter group, the Orange Volunteers, said it carried out the attack and warned of further violence.

Customers, including three Turkish lorry drivers, were left badly shocked after a grenade exploded outside the window.

IRA 'not behind killing'

The bar is owned by former Sinn Fein councillor Francis McNally, who said it was only because of reinforced glass that no one had been killed.

Eamon Collins: Mainstream IRA 'not to blame for murder'

At the same time, the widow of murdered IRA defector Eamon Collins has said she believes republican thugs outside the mainstream Provisional IRA were behind his death.

"I don't believe that the south Armagh IRA had anything to do with his death," Mrs Bernie Collins told BBC Northern Ireland's Spotlight programme.

"I feel that if they had wanted Eamon dead it would have happened before now and in a different manner."

Admitting involvement in the attack on McNally's pub, the Orange Volunteers, warned of more strikes against what it called the "enimies of Ulster."

The organisation has carried out a number of gun and bomb attacks on homes and businesses in the south Derry area in the past month.