State Department e-mail hacked?

• Official: The State Department detected "activity of concern" in an unclassified e-mail system


• Now its stepping up security during a system shutdown, the official says


• Officials haven't said who's responsible, say it's connected to recent White House hacking


• U.S. officials pointed at Russia after that hacking attempt

Washington (CNN) -- The U.S. State Department recently detected "activity of concern" in portions of its e-mail system, a senior official said Sunday.

Could it be a hacking attempt by a foreign government? U.S. officials aren't saying. But the State Department is now stepping up security of its unclassified network during a system shutdown, the senior State Department official said.

The activity was spotted in portions of an unclassified e-mail system, the official said, and there was "no compromise of any of the Department's classified systems."

Did Russians hack W.H. computer network?

Did Kremlin organize White House hack?

The official said the activity was related to hacking of White House computers reported last month.

After hackers broke into an unclassified computer network used by President Obama's top advisers, U.S. officials with firsthand knowledge said Russian hackers were the prime suspects.

Asked last month about the accusation that Russians were behind the White House computer hacking, a spokesman for Russian President Vladimir Putin responded, "Is there any evidence?"

"We've been hearing a series of groundless allegations against Russia recently," presidential spokesman Dmitry Peskov said. "So we can't take them seriously any longer unless there's proof."

CNN's Alla Eshenko, Pamela Brown and Catherine E. Shoichet contributed to this report.