The Trump administration told Russia on Thursday to stop what it said was harassment of international shipping vessels in the Sea of Azov and Kerch Strait aimed at trying to weaken Ukraine's economy.
"Russia's actions to impede maritime transit are further examples of its ongoing campaign to undermine and destabilize Ukraine, as well as its disregard for international norms," State Department spokeswoman Heather Nauert said in a statement.
The U.S. accused Russia of delaying commercial ships since April and stopping at least 16 commercial ships from reaching Ukranian ports.
Relations between Russia and Ukraine have deteriorated since Moscow illegally annexed Ukraine's Crimea region and provoked conflict between pro-Russian separatists and Ukrainian forces in eastern Ukraine in 2014.
Ukrainian President Petro Poroshenko observed Ukraine's Independence Day last week by announcing that his country had "cut all ties with the Russian Empire and the Soviet Union."
The Kremlin did not immediately respond to the U.S. request.