A court in Moscow has ordered the Russian protest leader Alexei Navalny to be placed under house arrest, after a request from investigators working on an embezzlement case.

Navalny and his brother Oleg face charges of stealing and laundering a total of 51m rubles (£840,000) from the cosmetics company Yves Rocher and a Russian firm.

Investigators had already made Navalny sign a pledge not to leave Moscow but asked for his restrictions to be stepped up to house arrest, arguing that he had repeatedly violated the restrictions imposed on him. As well as being unable to leave his home in the Moscow region, the new restrictions imposed by a district court mean Navalny will only be able to talk to relatives, investigators and his defence lawyers.

Crucially for a figure who has emerged as one of the main challengers to President Vladimir Putin through a widely followed blog, he will not be able to use the internet. Noir will he be able to send or receive letters or talk to the press.

The term of the house arrest is until 28 April but it can then be extended. "He will only be allowed to leave his home with the permission of investigators," his spokeswoman, Anna Veduta, wrote on Twitter.

In a separate embezzlement case, Navalny was given a five-year jail sentence in July last year, but released a day later. He and his supporters argue that, like his previous conviction, the current case is a ruse by the Kremlin aimed at eliminating one of Putin's most dangerous opponents from politics.

Navalny is serving a week-long administrative detention sentence handed out this week for disobeying police orders at a demonstration over the jailing of a group of activists opposed to Putin. He is due to walk free from that term on 3 March but under the court ruling he will then immediately have to begin the period of house arrest.