“It’s certainly a tough development at a tough time,” a United Nations official privately acknowledged.

The U.N. and Turkey are each trying to mediate discussions to restart Ukraine’s grain exports. But Turkey’s status as a neutral partner in the talks now appears to be in danger of being compromised in the eyes of Ukrainian officials. Kyiv has summoned Turkey’s ambassador in Ukraine after Ankara released a Russian-flagged cargo ship that Ukrainian authorities say is filled with “stolen” Ukrainian grain — Ukraine’s foreign affairs ministry estimates Russian forces have stolen at least 400,000 tons of grain from the country since the February invasion. The development threatens to damage relations between Ukraine and Turkey at a highly sensitive time, just days before another possible round of talks in Istanbul that aim to free millions of tons of food exports.

U.N. officials are also preparing for a potential meeting in the coming days, according to two people. But it’s unclear whether Russia or Ukraine will agree to attend. Western leaders have suggested a plan to guarantee safe passage for Ukraine’s food exports via the Black Sea is ready, but it requires Moscow’s final agreement.

Ukrainian Foreign Minister Dmytro Kuleba has publicly declined to say whether Ukraine will attend any possible talks in the coming days.

U.S. officials are not directly involved in negotiating with Russia to reopen the Black Sea for Ukraine’s food exports but they have been treading incredibly carefully amid the ongoing talks and are being briefed on developments by U.N. officials.

“We think all the preparations are in place and they could be concluded very soon, if Russia goes along,” Jim O’Brien, the State Department’s head of sanctions coordination and a top official overseeing efforts to unlock Ukraine’s food exports, said in an interview.

Russia appears at the very least to be putting Turkish President Recep Tayyip Erdoğan, a leading player in talks to broker the deal to free Ukraine’s agricultural exports, in an incredibly tough spot. Ukrainian authorities asked Turkey to investigate whether its stolen grain was coming into Turkish ports well before the first Russian-flagged ship left the Ukrainian port of Berdyansk, which is under Russian control, in late June. European officials say they’re looking into whether Ankara ran afoul of any Western sanctions.

A State Department spokesperson didn’t specifically comment on any Turkish role in the Russian-flagged ships carrying suspected stolen grain to Turkish ports. The person said the U.S. has seen reports of Russia stealing Ukrainian agricultural supplies, “including Maritime Automatic Identification System records that indicate Russian commercial cargo vessels are departing from near Ukraine with their cargo holds full of grain.”

“We are working with other countries to prevent the sale of grain that has likely been stolen from Ukraine,” the spokesperson added.

Turkey’s move to release the ship appeared to take several U.S. and European officials by surprise, who had previously said it was a “positive” step that Turkey had initially impounded the vessel.

“We are interested in looking at the outcome of the investigation of Turkish Authorities on the matter,” said Nabila Massrali, spokesperson of the European Commission for Foreign Affairs and Security Policy.

“Turkey as a candidate country is expected to align with the EU sanctions against Russia progressively, in particular due to the free circulation of products within our Customs Union,” Massrali said.

Moscow, meanwhile, played down Turkey’s investigation into one of the ships.

“The vessel has not been arrested but is undergoing standard procedures at the port,” Alexey Zaitsev, deputy spokesperson for Russia’s foreign affairs ministry, said on Wednesday. Russian state media say the ship is now back in Russian territorial waters.

Kremlin Spokesperson Dmitry Peskov also reiterated on Wednesday the Russian talking point that Western sanctions, not Moscow’s blockade, are to blame for the food shortages wracking many Middle Eastern and African countries reliant on grain shipments from Europe. Russian President Vladimir Putin met with the head of the state-controlled United Grain Company Dmitry Sergeyev that same day. Sergeyev, according to a Kremlin readout, told Putin that the major grain exporter had switched payments to the national currencies of “friendly countries,” pointing to several contracts in rubles for “Turkish partners.”

Mikuláš Bek, the Czech Republic’s EU affairs minister, told European lawmakers this week they need to “be firm in fighting disinformation by Russia.”

“By blaming the EU sanctions, Russia tries to divert the responsibility for the global food crisis,” Bek said. “It has to be repeated again and again: It is not due to the sanctions. The food crisis has been inflicted by Russia’s war of aggression against Ukraine.”

U.S. and European officials say they’ll continue to support the diplomatic efforts to resume Black Sea access for Ukraine’s food exports, but they’ll also keep working to expand overland routes to export grain from Ukraine. Those new routes have allowed Ukraine to ramp up its exports to around half their normal volume. Western officials say that’s eased a bit of pressure on the Black Sea talks, and somewhat diminished Moscow’s leverage over global food supplies.

“We’d still love to see Odesa open because that’s the right thing and it’s much easier,” said O’Brien, referring to Ukraine’s largest port. “But we do feel that land routes are denying Russia the ability to control whether people eat.”