MOSCOW -- Russian opposition politician Aleksei Navalny says he has been ordered not to leave Moscow as investigations continue connected to a criminal case launched over comments he made on social media.

Navalny wrote on Twitter that the investigator of the case told him about the restriction during questioning at the Investigative Committee on July 17.

“All this has been invented so that I couldn't travel to the regions” to campaign against candidates from the ruling United Russia party ahead of regional elections in September, he wrote.

While he was being interrogated, law enforcement officers searched the offices of his Anti-Corruption Foundation in southern Moscow.

Navalny also said that after the interrogation, investigators took him to the apartment he rents in Moscow and another apartment where he is registered as a resident.

The Investigative Committee said in mid-June that Navalny had been accused of libeling a World War II veteran who featured in a video clip with other Russians to express support for proposed constitutional reforms.

In a social-media post on June 2, Navalny, one of President Vladimir Putin's most vocal critics, described those in the video as “traitors,” “people with no conscience,” and “corrupt lackeys.”

The Investigative Committee said the comments contained “deliberately false information denigrating the honor and dignity” of the veteran.

Navalny faces penalties ranging from a fine of 1 million rubles ($14,255) to 240 hours of community service if convicted.

Earlier this year, Russian state-run media broadcast videos of WWII veterans, celebrities, and ordinary people expressing their support for constitutional amendments that were approved by a national vote on July 1.

Among other changes, the amendments allow Putin to seek two more presidential terms after his current term ends in 2024.

Navalny, 44, has been jailed several times in recent years, barred from running for president, and had a bid to run for Moscow mayor blocked.

In March, Navalny and his associate Ivan Zhdanov said that their bank accounts had been emptied and all their payment cards and those of relatives been blocked in what they described as a move to discredit and disgrace them.