KYIV, Feb 21 - President Volodymyr Zelenskiy on Saturday signed a decree imposing sanctions against Viktor Medvedchuk, the leader of a major Ukrainian opposition party and a close friend of Russian President Vladimir Putin.

The sanctions, which also target his wife, Oksana Marchenko, and six other individuals and 19 companies all believed to be tied to Medvedchuk, were approved by the National Security and Defense Council on Friday.

The sanctions freeze the assets of Medvedchuk and his wife for three years and prevent them from doing business in Ukraine. Most of Medvedchuk’s assets are under his wife’s name.

Ukraine has also said an oil pipeline that transports Russian oil products to Europe and is reportedly controlled by Medvedchuk will be nationalized.

The measures are the latest in a series of moves by Zelenskiy’s administration to go after Ukrainian individuals who critics say have close ties to the Kremlin.

The U.S. Embassy in Kyiv said it supported Ukraine’s “efforts to protect its sovereignty and territorial integrity through sanctions,” RFE/RL reported.

“Medvedchuk has been under U.S. sanctions since 2014 for undermining Ukraine’s security, territorial integrity, and democratic institutions,” it said in a statement.

Medvedchuk on Friday called the sanctions "illegitimate" and "illegal."

Ukraine on February 2 sanctioned Taras Kozak and three television stations he formally owns. Ukrainian media say the media assets, which aired pro-Kremlin propaganda, really belong to Medvedchuk.

Medvedchuk, who is a lawmaker and chairman of the pro-Russia Opposition Platform For Life (OPFL), criticized the moves against him and fellow party member Kozak. He vowed that he would not flee the country following the measures taken against him, which the Kremlin on Friday called "very alarming."

Medvedchuk is the head of the political council of the OPFL, which is the largest opposition group in the Ukrainian parliament. He is one of the party’s 44 deputies in the 450-seat legislature.

Medvedchuk has a warm personal relationship with Putin, who is the godfather of his daughter. The lawmaker was sanctioned by the United States in 2014 for undermining democracy in Ukraine.

Ukraine said it is investigating Medvedchuk and the other individuals on suspicion of “financing terrorism.” The sanctions are tied to exports of coal to Russia from a separatist-held region in eastern Ukraine.

Russia-backed separatists took control of parts of the Donetsk and Luhansk regions after Ukrainian protesters toppled pro-Kremlin President Viktor Yanukovych in 2014.

Profits from the illegal coal trade allegedly funded the three TV channels Medvedchuk reportedly owns. Ukrainian media reported about the illegal coal sales as early as 2016.

Ukraine also said on February 19 that it is seizing PrykarpatZakhidtrans, an oil product pipeline owned by offshore companies reportedly connected to Medvedchuk.

The OPFL has sharply criticized the sanctions and asset seizure, calling it "the destruction of Ukrainian democracy." (rfe/ez)