Feb. 8 (Bloomberg) -- A British journalist who reported that leaked U.S. diplomatic cables described Russia as a "virtual mafia state" has been expelled from the country, according to a statement from the Guardian newspaper.

Luke Harding, the Guardian's Moscow correspondent since 2007, was expelled in November then refused entry when he tried to return to Moscow last weekend, the paper said today in an e- mailed statement. Harding repeatedly traveled to areas where counter-terrorism operations were under way without notifying security services, Foreign Minister Sergei Lavrov said, according to state news service RIA Novosti.

The expulsion marks the first time a Western reporter accredited in Russia has been thrown out of the country since Angus Roxburgh, then a Sunday Times correspondent, was ejected from the Soviet Union in 1989, according to Paris-based Reporters Without Borders.

"This is a serious and shocking step, unprecedented since the Cold War," Elsa Vidal, head of the European and Central Asia desk at the media freedom watchdog, said by phone from Paris. "It's an attempt to force correspondents working for foreign media in Moscow to engage in self-censorship."

Harding, who wrote about corruption in Russia and in December 2007 reported that Prime Minister Vladimir Putin was worth $40 billion, is the co-author of "WikiLeaks: Inside Julian Assange's War on Secrecy."

"This is clearly a very troubling development with serious implications for press freedom," Alan Rusbridger, the Guardian's editor-in-chief, said in a separate statement issued late yesterday. "It is worrying that the Russian government should now kick out reporters of whom they disapprove."

Putin denied the Guardian report on his personal wealth in a televised news conference in February 2008, calling it "nonsense." People who write such things "dig it out of their noses and smear it on their papers," said Putin, who was president at the time.

Putin, 58, handed over the presidency to his protege, Dmitry Medvedev, in 2008, because of a constitutional ban on serving more than two consecutive terms. He hasn't ruled out a return to the Kremlin in 2012.

Russia's Foreign Ministry said today that Harding was sent back to London over the weekend because he broke immigration rules. Harding requested an extension of his journalist's accreditation and then left the country without receiving his credentials, the ministry said in a statement. The ministry didn't mention Harding's travel within Russia.

"In the event that the rules that apply to all foreign correspondents are followed," Harding won't have "any problems" returning to Russia, the ministry said.

The Guardian said Harding's failure to collect a press card before he left for London on an urgent reporting trip was no reason to refuse him entry to Russia.

"We have still not received an adequate explanation of why Luke Harding was deported on arrival at Moscow airport on Saturday, Feb. 5th, despite having a valid visa," the newspaper said. "This is part of a pattern of behavior by the Russian Foreign Ministry who first expelled Luke Harding in November 2010."

Harding declined to comment on Lavrov's comments when reached by e-mail.

U.K. Foreign Secretary William Hague asked Lavrov to provide an explanation for Harding's expulsion, the British Embassy in Moscow said. The U.K. was waiting for a reply, an embassy official who can't be identified because of government policy said before the comments released by Lavrov and the Foreign Ministry.

Russia denied a visa to William Browder, a U.S.-born British citizen, in November 2005. Browder, who runs Hermitage Capital Management Inc., was told at Moscow's Sheremetyevo Airport he wasn't allowed to enter the country, where he had lived for the previous decade. Russia retains the right to deny visas on national security grounds.

Thomas de Waal, a British journalist who has written extensively on Chechnya, was denied a visa to visit Russia in 2006.

Chechen rebel leader Doku Umarov late yesterday claimed responsibility for the Jan. 24 suicide attack that killed 36 people at Moscow's Domodedovo airport. "Hundreds of brothers" are ready to die to drive Russia from the Caucasus, Umarov said in a video posted on the Kavkazcenter.com website.

Ingushetia and Dagestan, the mainly Muslim North Caucasus regions, are near Chechnya, which has fought two wars of independence since 1995, are hotbeds of unrest because of poverty and corruption.