The Kremlin has hardened its stance against dissent in Russia by expanding the definition of treason to include critics of the state.

A new Bill submitted to the Duma, the Russian parliament, on Friday will leave people vulnerable to prosecution for acts considered to threaten not only national security but also the country's constitutional order. Critics said that it was designed to intimidate opposition to the Kremlin at a time of rising economic discontent.

Details of the Bill emerged as the man accused by Britain of murdering Alexander Litvinenko, the dissident former spy, said that anyone harming the Russian State should be killed. Andrei Lugovoy, who is now a member of the Duma, said that he would order the assassination of anyone considered a traitor if he were in the Russian President's shoes.

“If someone has caused the Russian state serious damage, they should be exterminated,” Mr Lugovoy, a former KGB officer, told the Spanish newspaper El País. “Do I think someone could have killed Litvinenko in the interests of the Russian State? If you're talking about the interests of the Russian State, in the purest sense of the word, I myself would have given that order.

“I'm not talking about Litvinenko but about any person who causes serious damage.”

Mr Litvinenko, a fierce critic of the former President Vladimir Putin, died in exile in London in November 2006 after being poisoned with radioactive polonium-210. Mr Lugovoy denies killing him.

The Bill defines treason as “a deed aimed against security of the Russian Federation, including her constitutional order, sovereignty, territorial and state integrity”. The present law restricts prosecutions to “acts aimed at damaging external security”.

The measure also threatens to revive the Soviet-era habit of placing under suspicion anyone who has contact with foreigners. It gives warning that people could be guilty of treason for “rendering financial or material and technical or consultative support to ... a foreign organisation”.

The amendment raises the spectre of people falling under suspicion for giving interviews critical of the Kremlin to foreign journalists.

The definition of foreign bodies is also being expanded to include international organisations, which the note said had sought repeatedly to obtain Russia's secrets through illegal methods.

A note to the Bill said that it would ease investigations by the Federal Security Service, the successor to the KGB. The Russian newspaper Kommersant headlined its report on the proposals as “Betrayal of the Motherland - the business of everyone”.

Mr Putin attacked foreign organisations when he was President, suggesting that many were fronts for Western governments to promote unrest. He imposed heavy reporting rules on non-governmental organisations, requiring them to obtain official approval of annual plans of work.

Boris Nadezhdin, a law lecturer at Moscow university and a senior official with Right Cause, a new Kremlin-approved liberal party, said that the latest reform was an “act of intimidation” drawn from the Stalin era. The authorities would be able to use the powers to suppress opposition activity.

Gennadi Gudkov, the deputy head of the Duma security committee, denied that the Kremlin could accuse anyone of treason, explaining that “not everyone has access to state secrets”.

Mr Putin's United Russia party holds two thirds of seats in the Duma so the Bill is certain to become law. The amendments were presented on the same day that the Duma restored the Soviet practice of allowing judges to decide cases against people accused of violent crimes and civil disturbances.

Police arrested 90 demonstrators in Moscow and 60 in St Petersburg on Sunday for staging anti-Kremlin protests. Garry Kasparov, the chess champion and critic of Mr Putin, and Boris Nemtsov, a former Deputy Prime Minister, founded a movement to try to unite democratic opposition to the regime.

President Medvedev ordered police chiefs last month to take harsher measures against social unrest and bring charges, saying: “Otherwise there won't be any order.”

Russian authorities fear that the economic crisis could spark protests as unemployment rises and incomes fall. There are expectations that the rouble will be devalued by as much as 25 per cent in the new year.

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