U.S. officials have reportedly obtained new and "highly credible" intelligence indicating al-Qaida or other terrorists are in the United States and are preparing to launch a major attack this summer.

According to a senior federal counterterrorism official who spoke to the Associated Press on condition of anonymity Tuesday, the intelligence does not include a time, place or method of attack. However, the official said the intelligence is among the most disturbing received by the government since the attacks of September 11, 2001.

The official said that of highest concern is the possibility that terrorists may possess and use a chemical, biological or radiological weapon that could cause much more damage and casualties than a conventional bomb.

U.S. Attorney General John Ashcroft and FBI Director Robert Mueller plan to hold a news conference Wednesday to outline the intensive efforts by law enforcement, intelligence and homeland security officials to detect and disrupt any potential terrorist plots. The FBI plans to dispatch a bulletin to some 18,000 state and local law enforcement agencies warning of the threat.