(Adds details, comment by U.S. ambassador)

KYIV, July 23 (Reuters) - Russian missiles hit infrastructure in Ukraine's port of Odesa on Saturday, a day after Russia and Ukraine signed a deal to reopen Black Sea ports to resume grain exports, the Ukrainian military said.

"The enemy attacked the Odesa sea trade port with Kalibr cruise missiles; 2 missiles were shot down by air defense forces; 2 hit the infrastructure of the port," the Operational Command South wrote on the Telegram mesaging app.

Russia and Ukraine signed a landmark deal in Istanbul on Friday to reopen Ukrainian Black Sea ports to export millions of tonnes of grain that has been stuck in Ukrainian silos during Russia's invasion.

Ukraine's foreign ministry spokesperson said the attack called into question agreements and promises made by Russia in Istanbul to the United Nations and Turkey, which brokered the deal.

In a statement, Ukraine's foreign ministry called on the United Nations and Turkey to ensure that Russia fulfills its commitments under the agreement for a safe corridor for grain exports from Ukraine's Black Sea ports.

Russia's defence ministry did not immediately reply to a request for comment about the attack.

U.S. Ambassador to Kyiv Bridget Brink called the strike "outrageous".

"Russia strikes the port city of Odesa less than 24 hours after signing an agreement to allow shipments of agricultural exports. The Kremlin continues to weaponize food. Russia must be held to account," she said on Twitter. (Reporting by Natalia Zinets Writing by Tom Balmforth Editing by Angus MacSwan and Frances Kerry)