Russia has suspended its participation in the Black Sea grain export deal, the Kremlin said on Monday.
The deal, brokered by the United Nations and Turkey last July, aimed to alleviate a global food crisis by allowing Ukrainian grain blocked by the Russia-Ukraine conflict to be exported safely.
It had been extended several times, but was due to expire on Monday. Russia had been saying for months that conditions for its extension had not been fulfilled.
"In fact, the Black Sea agreements ceased to be valid today," Kremlin spokesman Dmitry Peskov told reporters.
"Unfortunately, the part of these Black Sea agreements concerning Russia has not been implemented so far, so its effect is terminated."
Moscow has long complained that obstacles remained to its exports of grain and fertiliser, even though these were not directly sanctioned by the West, and presented a series of demands that it said had not been met.
"As soon as the Russian part of the agreements is fulfilled, the Russian side will return to the implementation of this deal, immediately," Peskov said.
He said the decision not to renew the deal was unrelated to an overnight attack on the bridge between Russia and Crimea, which he called a "terrorist act" and blamed on Ukraine.
The Ukrainian military suggested the attack could be some kind of provocation by Russia itself but Ukrainian media cited unidentified sources as saying that Ukraine's Security Service was behind the incident.
"These are absolutely unrelated events. Even before the terrorist attack, the position was declared by President Putin," Peskov said.