US officials have information suggesting al Qaeda has people in the United States preparing for a large-scale attack this summer, The Washington Post reported yesterday, citing sources familiar with the information.

Attorney General John Ashcroft and FBI Director Robert Mueller are due to hold at 2 p.m. (1800 GMT) news conference at FBI headquarters yesterday to give details of the threat, law enforcement officials said on Tuesday.

The Post said Ashcroft and Mueller would ask Americans to watch for several suspected al Qaeda operatives who may be in the country.

The concerns are driven by intelligence deemed credible that was obtained about a month ago indicating an attack may be planned between now and Labor Day, The Washington Post reported.

The Department of Homeland Security has no plans to raise the color-coded terror alert level, which is currently set at ?yellow? for an ?elevated? risk of attack, officials said on Tuesday.

Homeland Security Secretary Tom Ridge has warned since April of potential threats in the United States over the summer, including during this week?s Memorial Day holiday weekend.

Other events seen as vulnerable are the World War II Memorial dedication ceremony in Washington on Saturday, the Group of Eight summit in Savannah, Georgia, next month, the Fourth of July holiday and the Democratic and Republican national conventions toward the end of the summer. Officials said Mueller and Ashcroft would not announce any arrests or any new criminal charges at the news conference.

The Post said the FBI likely plans another public push to find Aafia Siddiqui, a Pakistani woman who has a doctorate in neurological science and has studied in the Boston area, as well as in Houston.