The Pentagon is stepping up the use of offensive spy versus spy operations to thwart espionage by foreign intelligence agencies or terrorist groups, senior defense officials said Tuesday.

They said the Defense Intelligence Agency is being given a larger mandate to pursue the "strategic offensive counter-intelligence operations" as part of a reorganization approved late last month.

"These are very tightly controlled, compartmented activities run by a small group of specially selected people within DoD (Department of Defense)," said Toby Sullivan, a senior Pentagon counter-intelligence official.

The objectives for the operations are set at high levels of the government and directed against "individuals known or suspected to be foreign intelligence officers, or connected to foreign intelligence or terrorist activities," he said.

Conducted clandestinely, the operations are not intended to catch spies but to turn their operations to US ends, according to the officials, who briefed reporters at the Pentagon.

"There have been some spies caught because of someone else making a mistake and us picking up on it," Sullivan said. "But by and large these are not run to identify spies.

"These are run to thwart what the opposition is trying to do to us, and to learn more about what they are trying to get from us," he said.

The DIA can conduct the operations inside the United States as well as overseas provided "it is against a foreign intelligence officer, not a US citizen," Sullivan said.

It also can operate in cyberspace.

"Quite frankly, from (the perspective of) an offensive capability, it provides us another venue to perhaps engage the enemy," he said.

"You have people using the Internet to meet and talk, and speak to each other," he said. "So you have that opportunity for folks to meet as much as you have opportunities for folks to meet in a restaurant."

The DIA was given authority to conduct the operations for the first time two years ago on a trial basis.

Sullivan said the agency's capacity to run them have been built up over that time. "They performed admirably," he said, refusing to provide further details.

The agency now has formally been given authority for them under a reorganization that has combined counter-intelligence and human intelligence in a single center in the DIA.

The DIA joins three other Pentagon agencies that are authorized to run them -- US Army counter-intelligence, the Naval Criminal Investigative Services and the Air Force Office of Special Investigations.

"We are an arrow in somebody's quiver," Sullivan said.

"They want us to go do something; we identify the possible threat; we work with those who are feeling the focus of the threat and they give us some ideas about objectives, at least at the operational level," he said.