Because the spycraft appears unsophisticated, Cohen said, "some old timers from the intelligence community speculated that the network is a decoy to mask a much more sophisticated espionage operation in the US."
Fred Burton, a former State Department intelligence agent who is now vice president at the security and consulting firm Stratfor, said the arrests after years of surveillance suggest that the network was nearing some key information or knew it had been compromised.
"The FBI didn't wake up Sunday morning and decide to take these folks down," he told AFP.
"Clearly, they were probably bumping up against something that was valuable," he said, adding that the spy ring may have "stumbled" onto "someone who has access to classified information or who is a defense contractor."
Because the suspects were not charged with espionage but with acting as agents of a foreign government, Burton said the investigation is not complete but that prosecutors "may build an espionage case" later against the group.
"I view this as a very sophisticated Russian illegal operation. But having said that, I think the FBI did a wonderful job in ferreting these people out."
Burton said there was "a logical assumption" that more Russian agents and sleeper cells may be operating on US soil and that "one of the results of these takedowns is that you will rattle a few trees that will lead to other people or fill in other parts of other investigations."
The US Justice Department said the 10 "deep-cover" suspects were held on suspicion of seeking details of US nuclear weapons and foreign policy.
Five of the accused appeared in court in New York on Monday and some of the suspects are apparently Russian nationals. According to US documents, the spy ring had been under FBI surveillance for a decade.
The case nonetheless reads like a work of fiction, with a glamorous Russian female agent, "sleeper" cells and cloak-and-dagger secret drops in public places, as one might expect in the Cold War era, which ended with the breakup of the Soviet Union in 1991.
"It's not surprising that even when relations are good, countries will continue their intelligence programs against one another. It's what intelligence agencies do," said Olga Oliker, senior international policy analyst at Rand Corp.
But Oliker noted that the case still raises questions about why the network operated in various cities away from the center of US government.
"This particular program has been in place for some time so it's very possible that a certain amount of inertia is what kept it going," she said.
"This strikes me as an odd program, because it's a very organized, well thought-out long term effort that doesn't seem to be all that effective."
Heather Conley, director of the Europe Program at the Center for Strategic and International Studies, said the case has a "back to the future" feel but shows that foreign governments gather information even on allies to gain advantages in negotiating or other situations.
Even so, Conley said much of the information being gathered appeared to be "open source" or "something that an embassy would do."
Cohen of the Heritage Foundation said the Russian ring appeared "very much stuck in the Cold War" but remained cause for concern.
"We should be concerned about any espionage," he said. "Friends don't spy on friends."