* Documents showed private eye tracked three in U.S.-source

By Mark Hosenball

March 2 (Reuters) - Three people who believe they were targeted by a private investigator working for Rupert Murdoch's News of the World while they were in the United States are considering suing his company in U.S. courts, a source close to the case said.

The lawsuits would be the first litigation filed against Murdoch's News Corp empire in the United States and could mark a significant escalation in a scandal that has already shaken Britain's media and political establishment.

Murdoch's British publishing arm News International has already handed out millions of dollars in settlements to celebrities and others who had their voice mails hacked by its journalists.

The source said London police had showed the three people documents seized from Glenn Mulcaire, a private investigator who worked for Murdoch's now-defunct tabloid News of the World.

The documents indicated Mulcaire had collected phone numbers and other information on the targeted individuals when they knew they were in the United States, said the source.

The evidence - in the form of detailed notes Mulcaire took regarding assignments he received from journalists at the newspaper - does not prove the persons targeted by Mulcaire had their voicemail hacked, the source said.

In at least one of the cases, said the source, Mulcaire's documentation also included at least one U.S. telephone number.

In January 2007, Mulcaire and Clive Goodman, the News of the World's chief reporter on Britain's royal family, pleaded guilty to charges related to phone hacking. Both were sentenced to brief terms of imprisonment.

All legal actions to date regarding alleged phone hacking by Murdoch journalists have been brought in U.K. courts. Recently, Murdoch's British publishing unit has made strenuous efforts to settle with claimants before their cases come to trial.

However, Mark Lewis, an English lawyer who has represented some of the highest-profile phone hacking claimants, is expected to visit the United States in April to consult with American lawyers about the possibility of filing phone hacking lawsuits in the U.S. court system.

In September last year, Lewis told reporters he had talked to American lawyers about filing possible claims against News Corp in New York.

Lewis' high profile clients have included the parents of murdered schoolgirl Millie Dowler. Revelations that the News of the World had hacked her mobile phone sparked widespread outrage and pushed the hacking scandal back into the headlines.

Bloomberg News reported last month that U.S. telephone numbers had been found in notes related to hacking victims which police had seized from Mulcaire, including numbers for a Los Angeles agent and New York publicist for Charlotte Church, a Welsh singer.

Earlier this week, it was announced that Church and her family had settled a phone hacking claim against the News of the World for 600,000 British pounds in damages and legal costs.

Earlier this year, British actor Jude Law settled a phone hacking claim against the News of the World, saying that his phone had been hacked on numerous occasions between 2003 and 2006, including when he was at New York's JFK Airport.

Last summer, the FBI opened an investigation into possible phone hacking inside the United States.

The probe came after London's Daily Mirror, a competitor to Murdoch's Sun tabloid, said a U.S. private investigator had told it he had turned down a request from the News of the World that he hack into phone data of victims of the September 11, 2001 al Qaeda attacks on New York and Washington D.C.

A U.S. law enforcement source said that the FBI inquiry turned up no evidence of phone hacking in the U.S. by Murdoch journalists, though the FBI is looking into possible violations of the Foreign Corrupt Practices Act, an American law which bans questionable payments to foreign government officials.

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