OTTAWA -- The federal government has rebuffed Air Canada's plea to be compensated for a portion of the more than $100 million the airline says it has spent over the last five years to accommodate gun-toting sky marshals on its flights.

Newly released documents show the government dismissed the airline's concerns about costs and other aspects of the program earlier this year on the grounds that changes would "compromise public safety."

Established after the Sept. 11, 2001, attacks on the United States, the Canadian Air Carrier Protective Program involves placement of covert sky marshals, known as in-flight security officers, on select commercial routes to prevent planes from being commandeered by terrorists.

Details of the program -- including information about its scope and which flights have officers -- are a closely guarded secret.

The Canadian Press used the Access to Information Act to obtain a censored version of a secret Public Safety Canada memo prepared earlier this year for Steven Blaney, minister at the time, and an accompanying letter from a senior departmental official to Derek Vanstone, an Air Canada vice-president.

Air Canada had expressed concerns about the sky marshal program in 2013 and subsequently met representatives of the RCMP, Public Safety and Transport Canada, prompting the follow-up correspondence.