Ukraine has halted its drone attacks on oil tankers using the Russian port of Novorossiysk in the Black Sea after a request from JD Vance, the deputy U.S. presidential chief, according to the Ukrainian authorities, the Financial Times reported on Wednesday.

Based on this report, Washington’s request came last month amid U.S. concerns that Ukraine’s targeting of oil tankers carrying Kazakh crude oil would destabilize oil markets and harm American companies. That oil reaches the Caspian Sea Pipeline Consortium terminal in the same port via a pipeline.

The Financial Times added that Ukraine has agreed not to target the infrastructure of this consortium and non-Russian vessels, provided that those vessels are not subject to Ukraine’s sanctions and do not carry Russian oil or cargo.

A U.S. official told the newspaper that the U.S. government has warned Ukraine to stop attacking non-Russian vessels in the Black Sea.