The security services and the siloviki – hardliners with security service backgrounds – within the presidential administration wield vast power in the opaque system of government under Mr Putin. While analysts frequently offer guesses about murky power struggles within the Kremlin, it is extremely rare for such clashes to be made public from the inside.

In an open letter in the Kommersant newspaper on Monday, Viktor Cherkesov, the head of the Federal Drugs Control Service, warned that the security services were in danger of becoming embroiled in an "all- against-all" war for power and influence.

Mr Cherkesov wrote that the intelligence community provided a "hook" for Russian society to hang on to in the 1990s, saving it from destruction. But the intelligence "corporation" now has such a powerful role that "the fate of the country" is in the balance if this corporation becomes overwhelmed with internal turf wars.

Mr Cherkesov served for 25 years in the KGB and its successor agency, the FSB, including as a deputy to Mr Putin when the latter was director of the FSB in the late 1990s.

His letter seems to have been prompted by the arrest of three top-ranking officials from his service last week. The officials are currently being held in custody and have been charged with a range of offences, including extortion. Mr Cherkesov hinted that they were arrested as revenge for a corruption scheme they uncovered last year involving FSB operatives. But his letter went wider than that, calling into question the very nature of the siloviki and their influence on Russian politics.

"The President's circle is full of siloviki, and it's difficult to determine their spheres of influence, which often overlap," said Alexei Makarkin, a Moscow-based political analyst. "When they were all fighting the same enemies, such as Mikhail Khodorkovsky, their internal differences were put to one side. But now they have 'won' and control everything, they have started to fight among themselves."

Analysts say Mr Cherkesov is no longer part of Mr Putin's inner circle, which is another reason for the unprecedented decision to publish an open letter. "It's very unusual practice for high-ranking officials to go public like this, especially those from the security services," said Dmitry Badovsky, of the Institute for Social Systems. There has been no response from the Kremlin or the FSB yet, and Mr Cherkesov failed to turn up to the launch of an anti-drugs report yesterday. "It's clear that the authorities are keen for any further discussion of these issues to take place privately," said Mr Badovsky.

Mr Putin has indicated he will not change the constitution to seek a third term as president, but last week indicated he may stay on as prime minister. "Nobody knows what will happen in 2008, so everyone is trying to strengthen their position as much as possible in the build-up," said Mr Makarkin.

The letter has confirmed fears that, far from the Russian elites standing together behind Mr Putin, they are engaged in private turf wars. "This is the reason behind Putin wanting to keep control after next year," said Mr Makarkin. "He is the only person who has the authority to carry out a balancing act between these forces. Otherwise the country could descend into chaos."