(Reuters] – Gennady Tychenko, a close ally of Russian President Vladimir Putin was forced to resign from Novatek’s board on Monday following sanctions against him for Russia’s invasion of Ukraine.

Novatek, Russia’s biggest private producer of food, didn’t give any reason for Timchenko’s resignation. Timchenko’s representative, who has been on the board since 2009, refused to comment.

Last month, the European Union and Britain imposed sanctions against Timchenko as well as other billionaires who have ties to Putin.

According to Forbes magazine, Timchenko was already on the U.S. sanctions lists for Moscow’s 2014 annexe of Crimea. He had a net worth $22 billion and was Russia’s sixth richest billionaire.

Russia sent hundreds of thousands of troops into Ukraine Feb. 24, in an operation it called “special” to weaken its southern neighbor’s military capabilities, and expel people it considered dangerous nationalists.

In an attempt to stop Russia from withdrawing its forces, Ukrainian forces are resisting the West’s sweeping sanctions. 

Timchenko is a member of the Sibur petrochemicals company board. He was also co-founder and chief executive of Gunvor, a Swiss-based oil trader. After the United States placed sanctions on Timchenko, he sold Gunvor’s stake to Timchenko in 2014.

Timchenko claimed he was a proprietor of a couple trading businesses in St Petersburg and the vicinity in the 1990s when Putin was working in the mayor’s office.