WASHINGTON (AP) – Russia has fully restored its espionage capabilities against America after a period of decline following the Cold War, a senior American counterintelligence official said Thursday.

Joel Brenner, the head of the Office of the National Counterintelligence Executive, said America is concerned that Russia is continuing to ramp up its operations.

“The Russians are now back at Cold War levels in their efforts against the United States,” he said at an event held by the American Bar Association. “They are sending over an increasing and troubling number of intelligence agents.”

The comments come at a time of greater tension between the two countries, as Russian officials have expressed frustration at what they see as American foreign policy unrestrained by consultation with other world powers, including Russia. They have criticized the expansion of NATO into the former Soviet sphere of influence and American plans to install radar and interceptors in Eastern Europe as part of a missile defense program.

In turn, American officials have warned that Russia’s increased assertiveness in challenging American policy is complicating cooperation on important foreign-policy goals including counterterrorism, nuclear nonproliferation and democracy promotion in the Middle East.

However, both sides deny that the tension means a return to the Cold War. American officials have praised Russian diplomatic help in the six-party talks on nuclear disarmament in North Korea. Russia has also provided backing for American efforts to force Iran to suspend uranium enrichment by joining other members in the United Nations Security Council recently in voting to impose limited sanctions for the second time in recent months.

In angry comments at a conference in Munich last month, Russian President Vladimir Putin said America “has overstepped its national borders in every way” and that “the almost uncontained … use of force in international relations” was prompting countries opposed to Washington to seek to build up nuclear arsenals.

“The Russians have been reeling from being one of the world’s great superpowers to being something very different, and trying to build themselves up and show that they are going to have to be dealt with as a major power is part of their agenda,” Mr. Brenner said.