U.S. law enforcement agents on Thursday searched New York properties linked to Viktor Vekselberg, a sanctioned billionaire Russian oligarch, NBC New York reported, as Washington seeks to use sanctions and property seizures to pressure Moscow to stop its invasion of Ukraine.

A Reuters witness observed FBI and Homeland Security Investigations (HSI) agents haul boxes and safes out of an apartment building at 515 Park Avenue in Manhattan, where NBC said a property linked to Vekselberg was located.

Agents also searched a Vekselberg-linked property in Southampton, New York, NBC said.

Vekselberg could not be reached for comment. An FBI spokeswoman confirmed that agents were present at the Manhattan and Southampton addresses, but declined to comment further. An HSI spokeswoman declined to comment.

It was not immediately clear what the agents were investigating. Vekselberg has not been criminally charged in the United States.

Washington imposed sanctions on Vekselberg in 2018 over alleged Russian interference in the 2016 U.S. election, and in 2022 over his ties to Russian President Vladimir Putin.

The Kremlin denies interfering in the election and calls its actions in Ukraine a "special military operation."

Vekselberg owns the Renova group of companies, which operate in Russia's energy sector, according to the Treasury Department, which enforces sanctions.

Russian prosecutors arrested two Vekselberg associates in 2016 for bribing officials connected to a power generation project, the department said.

In April, Spanish police impounded Vekselberg's superyacht Tango at the behest of U.S. prosecutors, who had obtained a warrant to seize the vessel.

They accused Vekselberg of obfuscating his ownership of Tango, and tricking U.S. banks into processing transactions for it.

The yacht has since been moored off Palma on the Spanish island of Mallorca, according to Refinitiv Eikon vessel tracking data.