White House spokesman Scott McClellan says the United States is entering a serious threat period, and security measures have been increased.

He says there has been a flow of credible intelligence information pointing to the possibility of an attack. He says the information does not point to a specific target, method or time. But he says there are many high-profile events coming up and notes terrorists "like to have a dramatic effect."

Those events begin this weekend with the dedication of the new World War II Memorial in the nation's capital. The Group of Eight summit will follow in just a few weeks in Sea Island, Georgia. And the U.S. presidential election campaign intensifies with the party nominating conventions in July and August, voting in November and inauguration day in January 2005.

Mr. McClellan indicates there are no plans to increase the formal terrorism alert level in the United States, though he stresses law enforcement and homeland security officials are working non-stop to protect the American public.

Attorney General John Ashcroft and FBI Director Robert Mueller have scheduled a news conference (2 p.m. EDT) to talk about the matter. The White House spokesman says they will discuss specific individuals who pose a threat to the United States.