Ukrainian prosecutors are seeking the arrest of Viktor Medvedchuk, a close friend of Russia’s president Vladimir Putin and leader of Ukraine’s main pro-Russia party, on suspicion of offences including “treason” and “looting of national resources” in Crimea.

The development, announced by prosecutor-general Iryna Venediktova at a press conference and on Facebook on Tuesday, is likely to further stoke tensions between Kyiv and Moscow. It came after the pro-western administration of Ukraine’s president Volodymyr Zelensky imposed sanctions on Medvedchuk this year and shut three television channels linked to the multi-millionaire for allegedly spreading Russian disinformation.

It also followed Russia’s recent deployment of more than 100,000 troops along the border with Ukraine’s eastern regions, where Moscow-backed separatists are mired in a smouldering war with Kyiv, and in Crimea, the peninsula annexed by Russia in 2014.

The “notices of suspicion” announced by Venediktova amount to preliminary charges in the Ukrainian system. She also signalled the authorities were seeking the pre-trial arrest of Medvedchuk, whose location remained unclear.

“According to the results of the searches, the whereabouts of People’s Deputy [Medvedchuk] have not been established, and therefore the SBU [state security service] is taking appropriate measures to find him and hand him a request for detention,” Venediktova wrote in a Facebook post.

Zelensky did not immediately comment on the allegations against Medvedchuk.

Pre-trial detention in prison or under house arrest must be approved by a court. A person familiar with the matter said authorities intended to seek to detain Medvedchuk in jail.

Charges were also announced against Taras Kozak, a business associate of Medvedchuk and member of the pro-Russian Opposition Platform — For Life party.

Venediktova said both men had colluded to acquire offshore oil and gasfields off the coast of Crimea, thereby implicitly accepting the peninsula as Russian territory.

“Considering Crimea to be part of another state is not allowed . . . It is also not permitted to create an army of information clowns and puppet master them along one’s own anti-Ukrainian interests,” Venediktova wrote.

At the press conference, Ivan Bakanov, SBU chief, said Kozak and Medvedchuk had also given Russia “secret data on the location of a hidden military unit of the [Ukrainian] armed forces, its personnel, combat training . . . sort of a gift for the secret services of the Russian Federation”.

Kozak was currently in Russia and “doesn’t plan on returning”, Bakanov added.

In a statement, Medvedchuk’s party described the charges as “political repressions”.

Zelensky’s administration has claimed Medvedchuk’s pro-Russian activities were financed through businesses in Russia that he and his associates control.

Medvedchuk, who has also been the target of US sanctions since 2014, has routinely visited Russia for face-to-face talks with Putin since Crimea was annexed. Russia’s president is also godfather to Medvedchuk’s daughter.

“Viktor Medvedchuk is long known agent of Russian influence in Ukraine,” said Tetiana Shevchuk, a lawyer at Kyiv-based anti-corruption watchdog Antac.

Speaking on television on Tuesday, Ukraine’s president said most of the more than 100,000 Russian troops deployed to their shared border this year had not been withdrawn.

“We do not see a decrease there,” Zelensky said during a discussion about western-backed and domestic efforts to boost Ukraine’s defences.

“Ukraine does not want a war, but for peace, as paradoxical as it may sound, it must have a powerful and capable army,” he added.