A controversial new law widely expanding the definition of treason has come into effect in Russia on Wednesday despite President Vladimir Putin's promise to review it.

The new law widens the interpretation of treason to include activities such as financial or consultative assistance to a foreign state, an international or a foreign organization.

Rights activists have warned the new law is so vague that it would allow the government to brand any dissenter a traitor. They described it as part of a widening crackdown on the opposition after Putin's inauguration for a third presidential term.

While the previous law describes high treason as espionage or other assistance to a foreign state damaging Russia's external security, the new legislation expands the definition by dropping the word "external." It keeps the punishment of up to 20 years in prison used by the prevision law.

The law, drafted by the Federal Security Service, the main KGB successor agency known under its Russian acronym FSB, also introduced a punishment for up to eight years for simply getting hold of state secrets even if they aren't passed to foreign hands.

The FSB explained in a statement carried by the ITAR-Tass news agency that the new clause is intended to help better protect confidential information.

Putin, a KGB veteran, has clamped down on his critics following a series of major street protests against his rule with a series of repressive bills and arrests and searches of opposition activists

He promised Monday to have another look at a treason bill to avoid a broad interpretation of treason, but it became law despite his statement.