US officials insisted Tuesday that a cyber attack late last year did not compromise White House classified systems, but refused to confirm reports Russia was behind the breach.

"There was an event last year," said deputy national security advisor Ben Rhodes. "We have classified systems that are secure,"

"We don't talk about where cyber intrusions originate from."

CNN earlier reported that Russia was behind the October attack that originated at the State Department, but was confirmed to have hit the White House too.

National Security Council Spokesperson Mark Stroh told AFP the report was "speculating" on who was behind an attack that affected the unclassified "Executive Office of the President" network.

The Executive Office is made up of President Barack Obama's closest advisors, including the National Security Council and Council of Economic Advisors, as well as the Vice President's staff.

While separate from classified systems, that network is used to exchange sensitive information about White House activities, such as detailed breakdowns of the president's movements.

"Any such activity is something we take very seriously," Stroh said. "We took immediate measures to evaluate and mitigate the activity."

Obama recently ordered a new sanctions program that could block assets of US and foreign hackers and of companies that seek to profit from cyber attacks.

Obama said the threat from cyber attacks was a "national emergency."

"Starting today, we're giving notice to those who pose significant threats to our security or economy," he said.

China, Russia and Iran are seen as most active in the cyber warfare arena.