The White House acknowledged on Monday an attempt to infiltrate its computer system, but said it had thwarted the effort.

A White House official said the attack targeted an unclassified network. He said the attack was identified and that the system was isolated to prevent its spread.

He said there was no indication that any data was removed.

The official, who was not authorized to speak on the record about the attack, said there was no attempted breach of classified systems. The official described such "spear phishing," referring to an attack launched via infected emails, as "not infrequent."

A report on Fox News followed claims on right-wing blogs that Chinese hackers had targeted extremely sensitive White House computer systems, including ones used by the military to command the country's nuclear arsenal.

A White House official said that the system involved was not a sensitive nuclear system and that no evidence indicated that any information was actually taken.

"In this instance the attack was identified, the system was isolated, and there is no indication whatsoever that any exfiltration of data took place," a White House official said. "Moreover, there was never any impact or attempted breach of any classified system."

Last year, Google Inc. blamed computer hackers in China for a phishing effort against Gmail accounts of several hundred people, including senior U.S. government officials and military personnel.

The White House would not say whether the recent attack was linked to China.