Demonstrations in Khabarovsk are part of a three-week wave of opposition challenging the Kremlin.
All 176 people on board were killed when Iranian forces struck the Ukraine International Airlines Boeing 737 jet after takeoff in Tehran in January.
The protesters gathered in the Belarus' capital of Minsk to support opposition candidate Svetlana Tikhanovskaya.
The Belarusian State Security Committee, still known by its Soviet-era name KGB, said it detained more than 30 contractors from private Russian military firm Wagner outside Minsk, the country's capital.
Members of the Wagner group were allegedly plotting to destabilise the country ahead of next month's presidential election, Belta state news agency has reported.
Justice minister Zbigniew Ziobro has said his ministry would submit a request to the labour and families ministry to begin the process of withdrawing from the treaty, known as the Istanbul Convention.
Tens of thousands of people marched across the city of Khabarovsk on the border with China to protest the arrest of the regional governor on murder charges, continuing a wave of protests that has lasted for two weeks in a challenge to the Kremlin.
The dismissal of the editor-in-chief of the Hungarian news website Index.hu has increased concern that Prime Minister Viktor Orban's nationalist government is intensifying efforts to muzzle critical voices.
Belarusian leader Alexander Lukashenko government has cracked down on the opposition ahead of an upcoming ballot, detaining protesters and would-be candidates.
Moscow has played a significant role in propelling the conflict between the two neighbours by creating autonomous regions in Azerbaijan and drawing controversial borders.
Ukrainian police say an armed man who seized hostages on a bus in the western city of Lutsk has been detained and all people held have been freed unharmed.
The huge rallies in the city of Khabarovsk on the border with China present a growing headache for the Kremlin, observers say.
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