Kremlin critic Alexei Navalny was questioned on Friday by Russian investigators and his offices were raided by police in what colleagues called an attack on his anti-corruption campaigning.

Shortly before noon (0500 ET), Navalny, who led a protest movement from 2011 to 2012 against Vladimir Putin's rule, said on Twitter 12 policemen had escorted him to the investigators' offices.

Navalny, 38 is technically under house arrest but has taken an increasingly confrontational course with the Kremlin. He has defied the arrest order to join a street protest, cut off his monitoring tag and given an interview to a radio station.

Navalny remains one of the biggest thorns in Putin's side but appears to have little chance of mounting a serious challenge to the Kremlin leader, whose popularity is high.

The Investigative Committee, which answers directly to Putin, has opened up several criminal cases against Navalny. The latest charges of embezzlement him led to a suspended sentence on Dec. 30.

"Today we broke a record. Twelve people were waiting for me at my apartment building's exit," he wrote on Twitter.

"The order was to escort. They're taking (me) to the Investigative Committee."

After questioning at the committee, he and colleagues at his anti-corruption fund said masked men with guns had raided the organization's offices, opening its safe and going through records and computers.

"Four people are filming on cameras. No one has identified themselves," said Lyubov Sobol, a lawyer.

"They want to take away all the fund's equipment, including the volunteers' telephones, computers, flash cards, etc ... it's clear it's an attack on the fund," she said on Twitter.

Navalny was placed under house arrest almost a year ago during an investigation into charges that he stole 30 million rubles from two firms including an affiliate of French cosmetics company Yves Rocher.

He was given a suspended sentence in the case and has said the house arrest order no longer has any legal basis. His brother was jailed for three and a half years in the same case.