Henrik Montgomery, TT, Associated Press
Wilhelm Unge, chief analyst at Swedish security service SAPO, speaks during a press conference as SAPO released its annual report in Stockholm, Wednesday March 18, 2015. SAPO has accused Russia of conducting "extensive" espionage operations, using as many as one-third of its diplomatic staff in the country for clandestine intelligence gathering.

SOLNA, Sweden — Swedish security service SAPO on Wednesday accused Russia of using as many as one-third of its diplomatic staff in the Scandinavian country for clandestine intelligence gathering.

Offering an unusual glimpse into the hush-hush world of counter-espionage, SAPO chief analyst Wilhelm Unge described the Russian spies as "highly educated and often younger than during the Soviet era. They are driven, goal-oriented and socially competent."

Naming Russia as "the biggest intelligence threat against Sweden, followed by Iran and China," he said SAPO last year stopped several attempts by Russia to obtain Swedish technology for military purposes, but declined to give specifics.

The Russian Embassy didn't immediately answer an email seeking comment.

SAPO warned last year that Russia had stepped up its political, economic and military espionage in Sweden — which isn't a NATO member but cooperates closely with the alliance — amid deteriorating relations with the West over the Ukraine crisis.

"There are hundreds of Russian intelligence officers around Europe and the West. They violate our territory every day," Unge told reporters at SAPO headquarters in Solna, just outside Stockholm, at the launch of the agency's annual report.

"What's notable is that about one-third of the Russian diplomatic personnel are in reality not diplomats but intelligence officers," he said.

"Why don't we send them out?" he said. "Counter-espionage comes with the complication that we're following other governments. This becomes politics directly. So we don't own the decisions of who should or shouldn't be in Sweden. That's up to the government."

Sweden's Foreign Ministry didn't return calls seeking comment on the issue.