WASHINGTON, July 8 (Xinhua) -- The websites of U.S. government agencies including the White House, the State Department and the Pentagon have been under cyber attack, said the government on Wednesday.

State Department spokesman Ian Kelly confirmed to reporters at a press briefing that the state.gov website had been under attack since July 5, although "it's much reduced right now."

Kelly said that the U.S. computer emergency readiness team is working with experts of his department and other affected government agencies to try to resolve the problem.

However, the source of attacks can not be confirmed yet, the spokesman added.

The cyber assault on the White House site did not effect its day-to-day operations with preventative measures in place, said spokesman Nick Shapiro, adding that the site is "stable and available to the general public."

The Department of Homeland Security, which led the investigation into the attacks, confirmed that U.S. government and private sector websites had come under so-called "distributed denial of service" attack without identifying any of the targeted sites.

U.S. media quoted computer security experts as saying that U.S. government websites, including those of the White House, Pentagon and State Department, were targeted in a coordinated cyber attack which also struck sites in the Republic of Korea.