Oryol, Russia - Russia's security service said Thursday it had arrested a trans rights activist accused of "high treason" for supporting Ukraine, as lawmakers backed a bill banning gender transitions.

Authorities "stopped the illegal activities of a Russian citizen, resident of the Oryol region, involved in high treason for providing financial aid to the armed forces of Ukraine", the FSB security service said in a statement.

In a video of the arrest made by the FSB and shared by Russian state media, the suspect is seen being pinned against a wall by armed men in fatigues.

The suspect is heard calling out for help, before being handcuffed and bundled into a van.

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According to the FSB, the detainee was a trans man working for rights monitoring group OVD-Info. The person was accused of arranging transfers of money to organizations in Ukraine "in order to finance" the Ukrainian army.

The crime of high treason is punishable with life imprisonment in Russia.

The arrest was announced as a bill banning surgical and legal gender reassignment passed second reading in Russia's lower house of parliament, the State Duma.

"Medical workers are prohibited from carrying out medical interventions aimed at changing the sex of a person," the lower house of parliament said in a statement, quoting the draft legislation.

People who have already changed their gender will not be able to adopt children or act as guardians, the statement also said.

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The third reading of the bill is expected to take place on July 14.

Russia has for years been a notoriously unfriendly place for anyone who does not comply with the Kremlin's hardline views on "family values".

President Vladimir Putin has repeatedly railed against trans rights.

Since the start of its offensive in Ukraine, Russia has adopted a series of anti-LGBTQ+ measures.