Police in Northern Ireland have warned of possible terror attacks ahead of visits by Rishi Sunak and US President Joe Biden next week.
The PSNI says it has "strong" .intelligence suggesting officers could be targeted in Derry on Monday.
MI5 had recently raised the terrorism threat level in Northern Ireland to severe, meaning an attack is highly likely.
This followed the gun attack on senior detective John Caldwell in Co Tyrone, who has been left with life-changing injuries.
Police have blamed the New IRA for the attack.
Assistant Chief Constable Bobby Singleton said: "It's going to be a really significant weekend for the PSNI.
"There is also very strong community intelligence specifically coming forward in respect of Monday's events in Derry/Londonderry and a real concern that there may be attempts to draw police in to serious public disorder and to use that then as a platform to launch terrorist attacks on police as well.
"So going into our operation that's something that is very clearly right at the forefront of my mind, the minds of the commanders that will be delivering that and of course our officers as well."
PSNI Chief Constable Simon Byrne said that officers would be moved to frontline duties to counter any potential threats, in a policing strategy that he said had not been used in years.
Speaking in Belfast, Irish deputy premier Micheal Martin condemned the threat of a terrorist attack as "criminality in its worst form" and said it was "very evil people who are contemplating this".
The warning comes ahead of US President Joe Biden's much-anticipated visit to Belfast on Tuesday.
Mr Biden's trip, which will also include events in Dublin, Co Louth and Co Mayo, will have a strong focus on the 25th anniversary of the Good Friday Agreement, which falls on Easter Monday.
Easter Monday is the day dissident republicans traditionally mark the anniversary of the Easter Rising rebellion against British rule in 1916, with a parade set to take place in Derry.
Mr Singleton said while dissident republican intent to kill police officers remained the same, he said officers were concerned they may use public disorder in Londonderry as a platform to launch attacks.
"The intent remains the same. I think as I see it, it's the risk, it's the platform potentially, in particular, that public disorder may present," he said.
"We don't have to go too far back, sadly, to see precisely that kind of scenario playing out in Derry/Londonderry in the past.
"So that is absolutely something that's in the mind of myself and the police commanders as we approach that event, and it will be something that we'll have to keep under constant review depending on how things develop on the day."
When asked about whether guns or explosives could be used to target police in Londonderry, Mr Singleton said: "We've seen that in the past and, on that basis, we have to be prepared for that and we will be prepared for all eventualities on Monday."
Briefing the Policing Board in Belfast, the Chief Constable said the overall tone in both the operational threat and the resourcing picture facing the PSNI is "stark and sombre".
He said: "We are now dealing with a severe terrorist threat, which means that an attack is highly likely right across Northern Ireland.
"The thing to stress is the main focus of these attacks continues to be police officers, both on and off duty, and their families.
"It will also include prison officers and military personnel. The style of attack that we are dealing with and trying to frustrate is gun attacks and bomb attacks on these people by a small number of determined dissident terrorists."
Mr Byrne said the increased threat came at a time of "unprecedented policing demand" in Northern Ireland.
