Ms Breen received the claim of responsibility for the Massereene murders
A journalist has said she has been threatened with legal action if she does not reveal Real IRA information sources.
Suzanne Breen, Sunday Tribune northern editor, received the Real IRA's claim of responsibility for the murder of two soldiers at Massereene base in March.
She said she would not comply with police demands to reveal her contacts.
Police said they would use all possible legal means "to access information which may assist their inquiries".
Sappers Mark Quinsey, 23, from Birmingham, and Patrick Azimkar, 21, from London, were shot dead as they collected pizzas outside Massereene barracks in Antrim on March 7.
Ms Breen said police visited her in Belfast last week over the claim of responsibility for the soldiers' murders and an interview with a senior Real IRA representative in which the group admitted killing Provisional IRA informer Denis Donaldson and threatened to murder more soldiers and police.
In today's Sunday Tribune she wrote: "I won't be complying with the PSNI's demands.
"Compromising sources undermines the freedom of the press. Journalists and police do different jobs.
"Our role is to put information into the public domain. If a journalist becomes a gatherer of evidence or a witness for the state, they cease being a journalist."
She said she was given seven days to hand over information.
Jeremy Dear of the National Union of Journalists said the union would "stand firm" with Ms Breen.
"The right of journalists to protect their sources is a fundamental press freedom and must be respected," he said.
"The authorities must recognise the special nature of journalistic material and respect Suzanne Breen's right to keep her sources confidential."
A police spokesman said: "The investigation into this atrocity is active and ongoing. Police will use every possible legal means to access information which may assist their inquiries.
"All victims of the Massereene attack, their families and the community expect and deserve nothing less."