NEW YORK (CNN) -- Associates of Osama bin Laden might have plotted to assassinate President Clinton when he visited the Philippines in 1994, a U.S. official told CNN.

The United States was aware of the planned attempt before the president left for the Philippines and as a result, security around the president was intensified, the official said Tuesday.

Bin Laden's associates, which allegedly include World Trade Center bomber Ramzi Yousef, had been "looking into the feasibility" of assassinating Clinton, the official said.

Yousef, who was arrested February 7, 1995, in Pakistan, where he had lived for a time in a boarding house owned by bin Laden, was to have been the assassin, the official said.

What is not clear is whether the plot was ordered by bin Laden or whether his followers planned it on their own.

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Following his arrest, Yousef was returned to the United States and charged in the 1993 World Trade Center attack that killed six people and wounded 1,000 more. He was later convicted in a trial in New York.

In a 1997 interview, bin Laden told CNN that he did not know Yousef personally, only by reputation -- one of high-standing in Islamic circles.

Bin Laden charged with inciting violence

Law enforcement sources tell CNN that bin Laden has been charged in a sealed indictment with inciting violence against U.S. citizens prior to the recent bombings of the U.S. embassies in Kenya and Tanzania.

Also, the New York federal grand jury investigating bin Laden was presented with evidence of financial links between bin Laden and a Islamic group based in Queens, sources said Monday.

Al Mahajirou, a Queens affiliate of a London-based group by the same name, is believed to have been involved in money transfers with bin Laden.

The grand jury has been looking into links to various groups in New York, New Jersey and Michigan.

The United States accuses bin Laden of masterminding the bombing of the U.S. embassies in Nairobi, Kenya and Dar es Salaam, Tanzania.

The East African attacks prompted the United States to retaliate Thursday by firing missiles at a training camp for militants linked to bin Laden in eastern Afghanistan and at a pharmaceutical plant in Khartoum, Sudan.

Experts say bin Laden, the millionaire son of a Saudi construction magnate, has used his money to fund attacks against the United States. The U.S. State Department calls bin Laden "one of the most significant sponsors of Islamic extremist activities in the world today."