MOSCOW (Reuters) - A Russian court sentenced opposition leader Alexei Navalny to 30 days in jail on Monday after convicting him of breaking public protest laws, a move he said was illegal and aimed at stopping him leading a rally against pension reform next month.

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Navalny, who was detained by police outside his home on Saturday, was found guilty of breaking the law by organizing an unauthorized Moscow rally on Jan. 28 which called for a boycott of what he predicted would be a rigged presidential election.

Under Russian law, the time, place and size of such protests must be agreed in advance with the authorities who have a track record of rejecting applications to rally in central Moscow and of suggesting less prominent locations instead.

Navalny, who was barred from taking part in the March presidential election over what he said was a trumped-up suspended prison sentence, has been repeatedly jailed for going ahead with such protests anyway despite official rejections.

The 42-year-old politician, who told the court he would never give up trying to organize street protests, said on Monday he believed the authorities were jailing him now, more than six months after his alleged offence, to stop him taking part in a protest planned for Sept. 9 against plans to raise the retirement age in Russia.

That is the same day as Moscow elects a new mayor, a contest expected to be easily won by incumbent Sergei Sobyanin, an ally of President Vladimir Putin, and authorities have rejected an application by Navalny’s supporters to rally in central Moscow.

‘STRANGE TRIAL’

“This strange trial is happening with the single aim of not allowing me to take part in the protest,” Navalny told the presiding judge. “You and I both know it.”

As he was led out of the courtroom, he shouted out the date and time of the planned rally.

“Everyone come to the meeting,” he said.

Navalny is hoping to tap into public anger over government plans to raise the retirement age to 65 from 60 for men and to 63 from 55 for women.

Opinion polls show most Russians strongly oppose the plan, which has been seen as responsible for a drop in Putin’s approval rating in recent months, prompting speculation that the Russian leader, whom Navalny has likened to an autocratic tsar, may decide to dilute the reform.

Putin, who makes a point of never saying Navalny’s name aloud when asked about him, has dismissed him as a troublemaker bent on sowing chaos on behalf of the United States.

Navalny has used protests and corruption exposes of the sometimes gilded lives of government officials to mobilize support. But many Russians, who still get much of their news from state TV which either ignores or derides him, say they do not know who he is.