Explosive allegations of espionage that centre on a Canadian intelligence leak to Moscow have resulted in the expulsion of four Russian embassy staff members from their stations in Ottawa, CTV News has learned.

The expulsion of the Russian staff, who are alleged to have taken part in the scheme, reportedly occurred four days after Sub-Lt. Jeffrey Paul Delisle was arrested in Halifax.

Delisle, 40, is facing two charges under Canada's Security of Information Act, and sources say that Russia was the nation involved.

CTV's Ottawa Bureau Chief Robert Fife reported that four Russian embassy staff members were sent home as part of the growing fallout from the scandal, which was uncovered earlier this week.

Along with two unnamed embassy workers, Canada has sent Lt.-Col. Dmitry Fedorchatenko and Konstantin Kolpakov packing.

According to the Geoffrey O'Brian, the former CSIS counter-intelligence chief, the colonel was likely the spy master of GRU, which is Russia's largest foreign intelligence agency.

"It is classically the military attaché that are classically the group from which GRU officers come," said O'Brian.

But despite the expulsion reports, officials in Ottawa and Moscow are remaining tight-lipped about the growing scandal.

A Russian embassy spokesperson said that no one had been expelled, and added that the four staff members in question went home because their "term had expired."

Canadian officials, meanwhile, responded by saying that the matter was being dealt with by the legal system.

"The matter is before the courts. On a national security file like this, I am not inclined to comment," said a statement from the office of Foreign Affairs Minister John Baird.

But sources have told CTV News that Canada is downplaying Russia's role -- at least publicly -- to avoid a tit-for-tat escalation that could see Canadian diplomats expelled from Russia.

Ottawa is also concerned about keeping up relations, as Prime Minister Stephen Harper is due to visit Russia later this year.

But the fallout from the scandal may not dissipate anytime soon.

"Sources say Delisle undoubtedly had access to current operational intelligence," Fife reported.

Sources say that the information could include sensitive data on underwater dead zones, which would allow Russian submarines to penetrate sensitive areas, in addition to information about navy ship movements in the Arctic and the Middle East.

Weapons system information may also have been leaked, sources said.

"But the real worry is the nightmare scenario," said Fife. "Did he have access to classified information, classified as beyond secret?"

That could include international communication signals from Canadian and American spies working in secret locations abroad.

"If he had access to that information, sources say this would be a goldmine for the Russians," Fife said.

The Russians allegedly recruited Delisle in 2007, when he was working as a naval intelligence officer in Ottawa.

Later, he would be transferred in Halifax, where sources say he handled information from a secret Canada-U.S. data system.

None of the allegations against Delisle have been proven in court.

Canada has reportedly been reassuring key allies behind the scenes, and the U.S. hasn't publicly issued any reason for concern.

Towing that line, Washington's point man in Ottawa said this week that Canada remains a chief friend of the U.S.

"I'm not going to comment on intelligence information," said Ambassador David Jacobson. "All I really want to say is that Canada is a trusted ally and partner of the U.S."

Delisle is in custody and will be in court on Wednesday.