Police forces across Scotland have been placed on alert in case suspected gunman Raoul Moat manages to cross the border into Scotland.
The move came after detectives in Northumberland admitted he may have managed to slip out of their exclusion zone.
Detective Chief Superintendent Neil Adamson said: "There is information that has come to our attention that has led us to conclude there is a wider threat to the public.
"From day one the key priority, the main priority, has been the protection of the public and that has always been the case."
He said: "While the search is now focusing on the Rothbury area, I am mindful of the potential for Mr Moat to have fled the area.”
Mr Adamson also revealed that two more men had been arrested in the Rothbury area last night on suspicion of assisting an offender.
Two other alleged accomplices appeared before Newcastle magistrates on Thursday morning accused of being part of Moat's conspiracy to hunt down and kill policemen.
Lothian and Borders and Strathclyde police were both being kept briefed on developments as the sixth day of the search continued, after detectives admitted there was a possibility he could have managed to escape from the police search zone. Hundreds of armed police surrounded the Northumberland village of Rothbury on Tuesday after a car Moat was said to have been using was found there. Two men, who were believed to have been hostages of Moat, were later found and arrested.
Detectives also found an abandoned tent just outside the village, believed to have been used by Moat. However, he has continued to evade them since and it has now been suggested he may have escaped the police exclusion zone, which ends 14 miles from the Scots border.
Detective Chief Superintendent Neil Adamson said: "We believe Mr Moat to be a measured individual who appears to carefully plan his actions and is comfortable in an outdoor environment.
"While the search is now focusing on the Rothbury area, I am mindful of the potential for Mr Moat to have fled the area.”
A Strathclyde Police spokeswoman added: “All UK forces are aware of the operation currently under way in Northumbria.
“Should information become available that he is in the force area, the appropriate response will be taken.”
An ACPOS spokesman told STV News that the situation in Northumbria was being constantly monitored.
No Scots officers have been called in to assist the Northumbria force so far, however, a specialist network known as the Police National Information Coordination Centre (PNICC) has been activated to ensure that every police force in the UK is briefed on the manhunt. A team of Scots police is currently liaising with that operation.
Moat was released from Durham Prison a week ago. He immediately posted a message on Facebook, saying: "Just got out of jail, I've lost everything, my business, my property and to top it all off my lass of six years has gone off with the copper that sent me down. I'm not 21 and I can't rebuild my life. Watch and see what happens."
Two days later, he is believed to have gone to a house in Gateshead and shot his ex girlfriend Samantha Stobbart, leaving her seriously injured. He then killed her new boyfriend, karate instructor Chris Brown. Police also believed him to have taken two men hostage.
Then, on Sunday, police officer David Rathband was shot in the face in an "unprovoked attack" while he sat in his patrol car in Newcastle. He is now said to be in a stable condition.
Moat later sent a letter to police, saying he had declared war on them and vowing to claim more lives.
On Thursday, armed officers and dog handlers were continuing to carry out thorough searches of the Rothbury area.
Temporary Deputy Chief Constable Jim Campbell said: "I'd like to thank again the residents of Rothbury for their support and patience at what is an unprecedented level of activity for them to see in their rural location.
"The searches in this area have proved a particular challenge due to the open farmland and dense woodland and officers are continuing in their efforts today. I'd like to reassure the public that we are doing everything possible to locate Moat and bring this investigation to a conclusion.
"Although much of the investigation centres on Rothbury, the events in this area are just one part of a complex investigation and activity continues across the force."
Meanwhile, the two men who were believed to have been held hostage by Moat have appeared in court, accused of being "part and parcel" of his plan to hunt down and kill policemen.
Karl Ness, 26, and Qhuram Awan, 23, who were arrested on Tuesday, have been charged with conspiracy to commit murder and possessing a firearm with intent.
At Newcastle Magistrates Court on Thursday, it was alleged that Ness was with Moat when he shot Samantha Stobbart and killed Chris Brown.
Ness, from Dudley in North Tyneside, and Awan, from Blyth in Northumberland, were remanded in custody.
Reporting restrictions were lifted for the hearing at which prosecutor Paul Simpson alleged that the men supplied Moat with the gun he used in the shootings.