Turkey and Russia have reached a tentative deal to restart shipments of Ukraine’s agricultural products from a key Black Sea port, but Kyiv remains skeptical of the proposed pact, according to people familiar with the discussions.

Turkish President Recep Tayyip Erdogan’s government has offered military help to clear mines off the coast of Odesa and escort grain ships but Ukraine has yet to endorse the plan, worried that removing defenses could leave the vital port open to Russian attack, the people said, speaking on condition of anonymity to discuss matters that aren’t yet public. Turkey hopes that a United Nations endorsement of the proposal could allay security concerns, the people said.

Ukrainian President Volodymyr Zelenskyy said Kyiv wasn’t invited to talks on the deal set for Ankara this week. Russian Foreign Minister Sergei Lavrov, who is scheduled to visit the Turkish capital Wednesday for discussions, said Monday he’s optimistic that military officials can work out a solution.