A second London lawyer is understood to have started exploring the possibility of legal proceedings over alleged phone hacking across the Atlantic. This lawyer, who declined to be named because proceedings had not been filed, claimed there was "considerable evidence" that a celebrity client had had voicemail messages intercepted by the now closed News of the World while on US soil.

The fresh legal moves mark a broadening of the attack on Murdoch's media empire, whose multimillion-dollar US headquarters has so far remained untouched by the scandal that has engulfed the group's UK newspaper operation.

The potential US lawsuits are understood to relate mainly to public figures who believe their phones were hacked while in America, where voicemail interception could constitute a violation of US telecommunications and privacy laws.

Lewis will next week begin discussions with his New York-based legal partner Norman Siegel, former director of the New York Civil Liberties Union, over the details of US law as it applies to phone hacking.

The negative attention garnered by the scandal eventually reached the United States, where News Corporation is headquartered and operates multiple media outlets. The Federal Bureau of Investigation launched a probe on 14 July 2011, to determine whether News Corporation accessed voicemails of victims of the 9/11 attacks. On 15 July, U.S. Attorney General Eric Holder announced an additional investigation by the Department of Justice, looking into whether the company had violated the Foreign Corrupt Practices Act.

Sen. John D. Rockefeller IV (D-W.Va.) on Wednesday asked Lord Justice Brian Leveson -- who is leading a British judicial inquiry into the scandal in Britain -- to turn over any findings that indicate if U.S. laws were broken by journalists or other employees of News Corp., the conglomerate Murdoch controls.

Rockefeller is chairman of the Senate commerce committee, which has broad oversight of American businesses and the Federal Communications Commission. An aide to Rockefeller stressed on Thursday that he hasn't called for an official committee investigation of New York-based News Corp. and that he simply wants information that may have surfaced during the Leveson inquiry.

The Justice Department and FBI are in the midst of two investigations into the hacking scandal. One seeks to learn if any News Corp. employees engaged in phone hacking in the United States; another is aimed at determining whether bribes paid to British officials by journalists at two News Corp. papers, the now-defunct News of the World and the Sun, for newsworthy information constituted a breach of a U.S. anti-bribery law, the Foreign Corrupt Practices Act.