Police in Northern Ireland have warned the public to be vigilant over the Easter weekend because of the "severe threat posed by terrorists".
Security checkpoints and patrols are being stepped up as a result.
On Saturday, detectives investigating dissident republican activity said they found a "substantial" amount of guns and ammunition in south Armagh.
Three men have been arrested in connection with the discovery on Friday near Keady.
The Police Service of Northern Ireland said the arrests were a joint operation with police in the Irish Republic.
'Single objective'
The BBC's Mark Simpson in Belfast says it is feared dissident republicans are preparing to attack police officers over the Easter holiday period.
Three weeks ago Northern Ireland police officer Constable Ronan Kerr, a 25-year-old Catholic, was killed in a car bomb attack and it is now believed there may be other attacks.
The police have warned the public to be vigilant and asked for more help in catching those involved in violence.
The message from the police to people in Northern Ireland is "help us to protect you".
A PSNI spokesman said: "Dissident terrorist groups are continuing to identify officers and target them with the single objective of killing them.
Election campaign
"And, in so doing, their reckless actions will also put the lives of our wider communities at risk.
"We ask for patience with their [the public's] officers if they are inconvenienced due to police activity."
The recent increase in dissident republican activity coincides with the Northern Ireland Assembly election campaign.
The dissidents do not have a political wing fighting the election and they seem interested only in violence, our correspondent says.
Police said they had made a "number of significant arrests" in the south Armagh area in relation to dissident republican activity.
Officers said the arrested men were taken to Antrim serious crime suite for questioning and the investigation was continuing.
source : bbc.co.uk
