The US has released details of seven people suspected of being involved in an al-Qaeda plot.
FBI chief Robert Mueller said a number of events, including the 4 July celebrations, the Republican and Democratic national conventions, and November's presidential elections could be at risk of attack.
Meanwhile Attorney General John Ashcroft said all of the seven people named presented a "clear and present danger".
The FBI has published the names and photos of the suspects and asked for the public's help in tracking them down.
Fazul Abdullah Mohammed
Born in the Comoros Islands, Fazul Mohammed is believed to be al-Qaeda's ringleader in East Africa. He was indicted in a New York court in September 1998 for his alleged involvement in the bombings of the US embassies in Nairobi and Dar es Salaam on 7 August of that year in which hundreds died.
A $25m reward is being offered for information leading to his apprehension or conviction.
He is in his early 30s, described as being "very good with computers" and apparently likes to dress casually and wear baseball caps.
Ahmed Khalfan Ghailani
Born in Zanzibar, Ahmed Ghailani is the second suspect mentioned by the FBI to be indicted for the US embassy bombings in December 1998.
A $25m reward is also being offered for him.
He is in his early 30s, and goes by the nicknames "Foopie" and "Ahmed the Tanzanian".
Adnan G El Shukrijumah
Born in 1975 in Saudi Arabia, Adnan Shukrijumah has lived in the US for 15 years.
A fluent English speaker, he is alleged to have been involved in terrorist planning with al-Qaeda leaders overseas and scouted sites across the US which might be vulnerable to attack. He has been sought by the FBI since the interrogation last year of al-Qaeda senior planner Khalid Sheikh
He carries a passport of Guyana, where his father was born, has many aliases and may be carrying Saudi, Trinidadian and Canadian documents as well. He has a pronounced nose and is asthmatic.
A reward of $5m is being offered for him.
Adam Yahiye Gadahn
Born in the US in 1978 and also known as Adam Pearlman, Adam Gadahn has not been linked to any specific terrorist activities, but the FBI is seeking him for questioning.
He is said to have had a Christian background, having grown up on a California goat ranch before converting to Islam in his teens. He was expelled from a mosque in California and sentenced to two days in jail for attacking an employee.
He is thought to have later trained at an Islamic militant camp in Afghanistan and done translations for al-Qaeda.
Born in 1972 in Pakistan, Aafia Siddiqui studied as an undergraduate and postgraduate in Massachusetts, and is also thought to have spent time in the Maryland suburbs of Washington.
She apparently returned to Pakistan after 11 September 2001 attacks on America with her husband and three children and has not been heard of since March 2003.
She is believed to be a "fixer", someone with knowledge of the US offering support to al-Qaeda operatives. Her husband, Dr Amjad Mohammed Khan, is also wanted for questioning.
Born in 1965 in Tunisia, the suspect has Canadian citizenship and his last known address was in Montreal. He allegedly appeared in a video suicide message seized in Afghanistan at the home of Mohammed Atef, the alleged al-Qaeda military chief killed in a US air strike in 2001.
He was reportedly chosen for flight training for a second attack on the US.
Born in Kuwait in 1963 of Egyptian and Syrian parentage, Amer Maati is a licenced pilot with Canadian citizenship.
US officials say he is believed to have discussed hijacking a plane and flying it into a building in the US.
He is said to require corrective lenses and might be wearing spectacles.