UN Secretary-General Antonio Guterres will travel to Istanbul later on Thursday, a UN spokesperson said as United Nations and Turkish officials seek to get a deal with Russia and Ukraine in writing to resume Ukraine's Black Sea grain exports.

"The situation remains a little bit fluid, so I can't really say when something will be signed," deputy UN spokesman Farhan Haq told reporters in New York. "We're not quite there yet."

The United Nations and Türkiye have been working for two months to broker what UN Secretary-General Antonio Guterres called a "package" deal - to resume Ukraine's Black Sea grain exports and facilitate Russian grain and fertilizer shipments.

(With input from Reuters)