A Facebook page has been shut down after claims it was an attempt to set up police officers in Northern Ireland for assassination.
The page, Crown Forces Watch, accused the police of carrying out a "campaign of intimidation and harassment" against Irish nationalists and called for people to post details of security operations and pictures of police officers.
It was inaccessible on Thursday.
"Clearly this is an attempt to gather information ... which I am in no doubt will be used in attempts to target police officers for murder," said Terry Spence, chairman of the Police Federation of Northern Ireland.
The police service said it was investigating the web page.
"We are aware the site has been closed down and we are continuing to making inquiries," a spokesman said.
The page appeared on the social networking site after a series of raids and arrests in Tyrone and Derry last week as part of an investigation into the murder of a Catholic police officer. All those arrested were released without charge.
The Facebook page claimed the men had been the victims of police harassment and intimidation and called for a response from the Irish nationalist community.
Most Irish nationalists, who want the British-controlled province to unite with the Republic of Ireland, support the police and are in favor of a 1998 peace deal that ended Northern Ireland's sectarian conflict.
A small minority, however, continue to oppose peace and target police officers in a sporadic but sometimes deadly campaign of violence.
Police raids remain controversial in nationalist communities, however, given memories of harsh treatment before the peace deal and the province's Deputy First Minister Martin McGuinness, a former nationalist guerrilla leader, criticised the police operation as "heavy handed and reminiscent of the bad old days."