Aivo P
© Priit Murk/ERRAivo Peterson
Estonian authorities announced on Friday that politician Aivo Peterson had been arrested on suspicion of activities against the state, along with two other individuals whose names were not released. The Baltic country's security service detained Peterson in the town of Narva-Joesuu, on the border with Russia.

Two Estonian citizens and one Russian national with permanent residence were detained, Security Police spokesman Harrys Puusepp confirmed to local media, identifying only Peterson by name. Puusepp did not offer any details about the charges against them, saying only that the state prosecutors were investigating them for "creating associations against the Estonian Republic."

Peterson is a prominent member of Together (known in Estonian as Koos, and in Russian as Vmeste), a leftist political movement advocating the peaceful coexistence of Estonians and Russians. He ran for parliament as a candidate of the Estonian United Left in last week's election. His arrest amounts to government repression, Together activist Andrey Pozdnyakov told the outlet Postimees.

Estonian outlets, such as Postimees and the state broadcaster ERR, described Peterson as a "pro-Kremlin activist" and accused him of making "pro-Russian statements."

In late February, Peterson traveled to Russia and a photo of his visit to Donetsk appeared on social media. Interior Minister Lauri Laanemets said that the politician must have collaborated with Russian intelligence in order to get so close to the battlefield, and declared him a security threat to Estonia. Border security reportedly detained Peterson for several hours on March 6, when he returned from Russia, but eventually released him.

Russian speakers make up about a quarter of Estonia's population of 1.3 million. The Baltic state, which is a member of the EU and NATO, has adopted a hard line towards Moscow over the conflict in Ukraine. In recent months, Tallinn has advanced the proposal to curtail Russian-language education, and said even the Ukrainian refugees would need to learn Estonian if they wanted to stay.

The opposition has accused Prime Minister Kaja Kallas of "stealing" the most recent election, which included a day of in-person voting on March 6 after a week of voting online.