A total of 1,643 people were arrested in fresh protests on Sunday across Russia demanding the release of opposition leader Alexey Navalny, monitoring groups say.

Despite intense measures taken by police, thousands of people, mostly high school and university students, attended the demonstrations held across many cities of Russia.

The streets in Moscow, where the protests are being held, were closed to traffic. Police also set up barricades with many police vehicles.

Moscow police also closed car parking lots and some metro stations.

Cafes, bars and restaurants were closed and alcohol sales were banned between 9 a.m. to 11 p.m. local time (0600-2000GMT).

Some 338 people were arrested in Moscow, according to human rights organizations in the country.

Yulia Navalnaya, the wife of the detained politician, was also arrested during the protests.

Some demonstrators gathered near the Matrosskaya Tishina Prison, where Navalny is currently being held, and chanted slogans against the government.

The Russian Interior Ministry said in a statement that the demonstrations were unauthorized.

The ministry urged Russian people not to participate in the demonstrations as they are open to provocations.

Navalnay, 44, was jailed on his return to Russia after spending months recovering in Germany from a poisoning attempt.

He blames the Russian secret service for the attempt to kill him with a nerve agent, a charge Kremlin denies./aa