MOSCOW - Russia’s Kommersant business daily said Friday it had asked the police to probe a Kremlin youth group for alleged involvement in repeated hack attacks on its website. The popular broadsheet vanished from the Internet for several days in 2008 after publishing an unflattering article about a group of young supporters that formed around Vladimir Putin shortly after he became president in 2000. The Kremlin has used the Nashi (Ours) movement to stage flashy campaigns in support of causes promoted by Putin - now prime minister but who hopes to regain his old job in March polls - and to attack some of his political foes.

But Kommersant said at the time that the movement was losing the Kremlin’s favour and was about to lose its funding - a claim that was later denied.

The paper said in its Friday issue that it had obtain a copy of letters written by a Nashi press secretary in 2008 in which she discussed staging a “psychological and physical” attack on Kommersant.

Nashi denounced the claims and said the letters Kommersant alleged to be holding could not be admitted as evidence in court.

It added in a statement that Kommersant’s pursuit of the case “will be read as slander and accompanied by corresponding counter-suits.”

The Russian interior ministry declined to comment on Kommersant’s request to institute criminal proceedings against Nashi.

Kremlin critics frequently witness problems with their websites whose roots are usually difficult to trace.

The tiny Baltic state of Estonia saw the websites of some of its top state institutions and newspapers go down in 2007 during a dispute with Russia over a monument dedicated to Soviet soldiers who died in World War II.

Nashi had led a week-long siege of the Estonian embassy at the time but denied any involvement in cyber warfare.

The websites of top Russian media outlets and and an election monitoring group also went offline during fraud-tainted December parliamentary polls in which Putin’s ruling party won a narrow majority despite allegations of fraud.