Russian courts jailed one of the organisers of opposition protests for 10 days, fined another and gave the husband of a third a five-year prison term for fraud on Thursday in rulings the opposition said were a warning signal from Vladimir Putin.

The punishments fuelled anger over what Putin's critics say is a corrupt judicial system and are likely to heighten opposition fears of a crackdown following his election to a new six-year term as president on March 4.

The authorities are sending the latest signal, Garry Kasparov, a liberal opposition leader and former world chess champion, told Ekho Moskvy radio station.

People who continue to hope for some illusory political reforms ... are once again being reminded that Putin will rule without a glance at any laws, let alone at public demonstrations in Moscow.

The opposition has been warning of reprisals since Putin won a third term as president and riot police the next day detained hundreds of people who attended unsanctioned rallies or refused to leave after a protest that had been permitted in Moscow.

Anti-corruption blogger Alexei Navalny was fined 1,000 roubles (21.66 pounds) for refusing to go straight home after the rally in Moscow's Pushkin Square.

Shortly afterwards, another court jailed far-left leader Sergei Udaltsov for 10 days for disobeying police by addressing a small crowd in Moscow after a peaceful rally last Saturday.

As a sign of protest I am declaring a dry hunger strike, Udaltsov said after the verdict was announced, making clear he planned to refuse both food and water.

Hours later, Alexei Kozlov, whose wife Olga Romanova is part of a lobby group that has helped organise the biggest protests since Putin first rose to power in 2000, was found guilty of fraud in a business deal and sentenced to five years in prison.

Damn you, court! Romanova, a journalist, said as the verdict was read out. Dozens of Kozlov's supporters, who say the charges are simply a punishment for political activities, shouted at the judge: Shame on you!

DEFIANCE

Udaltsov and Navalny, both of whom are 35 and have cropped hair, are among the most prominent and outspoken figures behind protests that have at times brought up to about 100,000 people on to the streets of Moscow.

Navalny said the opposition would not give up its struggle to secure Putin's departure and free elections in protests that were initially sparked by alleged fraud in a parliamentary election on December 4.

There are hundreds of thousands, millions of people in Moscow who are dissatisfied that their votes were stolen. They will continue to go out on to the streets to protest, he said.

International monitors said the presidential election was slanted in Putin's favour. A poll released on Thursday by state-controlled agency VTsIOM found 44 percent of Russians believed the result was reliable and in line with the voters' will.

Romanova, whose lobby group represents relatives of suspects in economic crimes, said her husband plans to go into politics when he is freed.

He will serve a maximum of about two years in jail as he has already spent three years behind bars on the same charge of theft of shares, which he denies.

Kozlov, who addressed the most recent anti-Putin rally in Moscow on Saturday, had been freed from prison last September after the Supreme Court threw out his conviction and sent the case back to a lower court for retrial.

Denouncing Putin and President Dmitry Medvedev, who is expected to take his ally's current job as prime minister, Romanova said: As long as they are in power here, unelected and self-appointed, this could happen to anyone.

Kozlov's case had begun long before the protests started. Judge Tatyana Vasyuchenko said Kozlov had failed to prove that he had bought shares and not stolen them during the disputed business deal. Kozlov's actions and those of his colleagues had a criminal intention, she said.

Kozlov's great grandfather, Vasily Zarubin, was a spy who warned Soviet dictator Josef Stalin about Nazi Germany's intention to attack the Soviet Union in 1941 but was ignored.

Kozlov's grandmother was married to another famous spy, Naum Eitingon, who plotted the murder of Stalin's rival Leon Trotsky in Mexico in 1940.

OPPOSITION LOOKS TO REGROUP

The opposition, which wants more democracy, a fair and open legal system and an end to corruption, is trying to regroup and find a new focus following Putin's election for a third term as president, extending his rule until 2018.

That would be enough to keep the former KGB spy in power as long as Soviet leader Leonid Brezhnev, whose 1964-82 rule is widely seen as a period of political and economic stagnation. If re-elected in 2018, he could rule almost as long as Stalin.

Numbers fell sharply at the most recent protest in Moscow on Saturday, partly because of dismay at Putin's re-election and his refusal to offer major concessions, but also because of fears of clashes after mass detentions on March 5 at unsanctioned rallies and after a rally that had been permitted.

Some opposition leaders want a clear agenda and a grassroots focus on winning seats - and more political influence - in local elections. Others want the protest movement to mix firm demands on Putin's government with a clear agenda of its own.

Agreement on policy is hard for a group uniting liberals, nationalists, leftists and independent organisations but several protest leaders issued a statement on trade policy this week in a first sign of a new direction.

The protest organisers have suggested that reprisals will spur them on but are increasingly wary of Putin's intentions.

Putin does not know the words 'compromise' or 'concession' as the result of a political dialogue. He is accustomed to an endless monologue, and so he always chooses the harshest options for counteracting his opponents, Kasparov said.

(Additional reporting by Darya Korsunskaya, Steve Guterman and Gleb Bryanski, writing by Timothy Heritage, editing by Steve Gutterman)