Were the phone accounts of 9/11 victims or their families hacked by unscrupulous British journalists? The U.S. government this week mobilized its law-enforcement machinery to find out.

It may be chasing a mirage.

Concerns that reporters affiliated with Rupert Murdoch’s now-defunct British newspaper, the News of the World, pried into the phones of terrorism victims ran through Washington this week in the wake of a news report carried by another British paper, the Daily Mirror.

Six members of Congress, including three from the New York-New Jersey area, expressed shock and outrage. The FBI, prompted by the lawmakers, confirmed that it has begun to investigate the allegation.

But the Mirror’s story — the only one thus far to assert that the British hacking involved 9/11 victims — remains unsubstantiated and uncorroborated, and it has been reported exclusively by a British tabloid famous for sensational journalism.

No official in the United Kingdom or United States has confirmed the paper’s assertion that “9/11 victims may have had their mobiles tapped by News of the World reporters.” No media organization has turned up evidence to support that claim independently since the story broke late Monday.

The report appears to be based on a shaky foundation. The Mirror names no specific sources in its reporting, and it relies on a single anonymous second-hand source for its account.

The story also appears to undercut its central premise — that phones may have been hacked.

The anonymous source is quoted later in the story saying that the information about hacking came from a former New York City police officer (also unidentified), who said he was approached by News of the World reporters seeking phone records of victims and their relatives. The News reporters were particularly interested in obtaining phone records belonging to British victims, according to the Mirror.

In any case, the paper said, no hacking took place.

“The [former policeman] said he had to turn the job down,” the Mirror quoted its source as saying. “He knew how insensitive such research would be, and how bad it would look.”

Within a day of publication, the Mirror story ignited a firestorm in Washington.

Sens. Jay Rockefeller (D-W.Va.) and Barbara Boxer (D-Calif.) were the first to call for an investigation, asking Attorney General Eric Holder Jr. and Securities and Exchange Commission Chairwoman Mary Schapiro to look into Murdoch’s News Corp., which is bas ed in New York.

Rockefeller and Boxer said they were concerned about reports that police officials in Britain had been bribed by Murdoch’s reporters there to get information, potentially a violation of the Foreign Corrupt Practices Act. News Corp. is a U.S.-based company, so it is covered by that act, which makes it illegal for employees of U.S. companies to bribe foreign officials.

The senators also said, “Additionally, there are troubling reports that News Corporation may have illegally accessed phone records of victims of the 9/11 attacks, and the Senators urged authorities to investigate whether any United States citizens had their privacy violated by this alleged hacking.”

They were soon joined by New Jersey’s Democratic Sens. Frank Lautenberg and Robert Menendez and by Reps. Peter King (R-N.Y.) and Louise Slaughter (D-N.Y.) in calling for a law-enforcement investigation. King is chairman of the House Homeland Security Committee.

“It is revolting to imagine that members of the media would seek to compromise the integrity of a public official for financial gain in the pursuit of yellow journalism,” King wrote to FBI Director Robert Mueller. “The 9/11 families have suffered egregiously, but unfortunately they remain vulnerable against such unjustifiable parasitic strains.”

He also wrote, “I make this request not only as the Chairman of the House Committee on Homeland Security, but as a Member of Congress who represents a district that lost more than 150 constituents in those terrorist attacks. It is my duty to discern every fact behind these allegations.”

In addition, Rep. Bruce Braley (D-Iowa), a member of the House Committee on Oversight and Government Reform, wrote a letter to the panel’s chairman, Rep. Darrell Issa (R-Calif.), calling for an investigation.

The Daily Mirror, which has a circulation of about 1.2 million, is a feisty tabloid that in 2004 ran a headline calling Americans who voted for President George W. Bush’s reelection “dumb.” But it is still generally regarded as somewhat less sensational than the Sun, a top-selling tabloid owned by News Corp.

In 2004, the Mirror became enmeshed in controversy after it published photos that purported to show British soldiers mistreating Iraqi prisoners. The paper later admitted that the photos were fake and that it had been the victim of a hoax. The episode led to the resignation of its editor, Piers Morgan, who this year replaced Larry King as host of a nightly celebrity-interview program on CNN.

The Mirror declined to comment Friday on its story.

A spokesman for the Senate Commerce Committee, which Rockefeller chairs, said Friday that an investigation was warranted, but he emphasized the bribery aspect of the story rather than the alleged 9/11 hacking.

“Our concern is not limited to whether 9/11 victims had their phones hacked,” said the spokesman, Vincent Morris. “That’s gruesome and of limited journalistic value but, right now, it’s just one allegation. The bigger and more alarming question is how broadly News Corp. employees may have used phone hacking on other stories, on U.S. citizens or on U.S. soil, as part of regular newsgathering. That’s why we want an investigation.”

Press representatives for Lautenberg, Menendez and Boxer declined to comment on the record. King’s spokesman did not return calls seeking comment.

Several congressional sources said the issue was too explosive to ignore, despite its suspect origins. The New York area lawmakers are particularly sensitive to 9/11 families that are their constituents, they said.

“There may be nothing to it,” said one staff member, who spoke on the condition of anonymity in deference to his boss, “but we have to look into it to make sure.”

Staff writer Felicia Sonmez contributed to this report.