Ukraine is using U.S.-supplied cluster bombs in its defensive operations in Russia-occupied areas, a White House spokesperson said Thursday, as Russian strikes on Ukrainian port cities continued for a fourth night.

National security spokesperson John Kirby told reporters the U.S. had received feedback that the munitions, which arrived from the U.S. last week, were being used “effectively.”

Ukrainian authorities said Russian missile and drone strikes on southern Ukraine and port areas had continued overnight.

In his daily address, Ukrainian President Volodymyr Zelenskyy said nearly 70 missiles had been fired at Odesa, Donetsk, Mykolaiv, Zaporizhzhia, Zhytomyr and Kharkiv this week.

Since Monday, concerns have been growing over global food supplies following Russia’s suspension of the Black Sea Grain Initiative, which has provided a key export route since July 2022.

Wheat prices have moved sharply higher as the European Union’s foreign policy chief warned the move could imperil global food security.

On Tuesday, Russia’s Defense Ministry said it was carrying out a “mass retaliatory strike” for an attack on the Crimean bridge early Monday which it blamed on Ukraine.

Tensions are also mounting in the Black Sea after Russia said it would consider all vessels sailing toward Ukrainian ports on the Black Sea as military cargo carriers. Ukraine’s Defense Ministry said it “may” do the same from midnight Friday. It has not yet provided an update.