At least six ships including the Ikaria Angel -- chartered by the World Food Programme and loaded with 30,000 tons of wheat destined for an emergency response in the Horn of Africa -- left Ukrainian ports on Monday, according to a website that tracks marine traffic.
"Civilian cargo ships can never be a military target or held hostage. The food must flow," Amir M. Abdulla, the UN Coordinator for the Black Sea Grain Initiative, tweeted on Monday.
Monday's shipping schedule was agreed by the Ukrainian, Turkish and UN delegations, with Russia informed of the movements, the JCC said in a statement late on Sunday.
A source familiar with the matter said: "As a signatory to the agreement, they have been requested to take the necessary measures to ensure the safety of the vessels."
Turkey's defense ministry said talks were under way with the relevant parties for the agreement to remain in place. The grain deal is due to expire on November 19.
International officials had feared that Moscow would reimpose a blockade on Ukrainian grain, after Russia announced on Saturday that it was withdrawing from the U.N.-backed program that escorts cargo ships through the Black Sea.
Moscow said it was forced to pull out of the shipping deal after blaming Kyiv for explosions that damaged Russian navy ships in the Crimean port of Sebastopol on Saturday.
Ukraine has neither confirmed nor denied it was behind those blasts but says Russia's navy is a legitimate military target.
Turkish President Recep Tayyip Erdogan vowed to pursue efforts to keep the agreement in force despite Russia's moves.
"Although Russia acts hesitantly... we will resolutely continue our efforts to serve humanity," Erdogan said in a televised address.
"Our effort to deliver this wheat to countries facing the threat of starvation is evident. With the joint mechanism that we established in Istanbul, we contributed to the relief of a global food crisis," he said.
A separate deal signed with Russia allowed the export of Russian food and fertilizers, despite Western sanctions imposed on Moscow. But it was never implemented, to the dismay of Moscow, which has complained about the issue for weeks.
On Thursday, two days before Russia's suspended its participation in the deal, its ambassador to the UN Vassily Nebenzia told reporters that Russian exports must be allowed to go through before Moscow would commit to a deal extension.
This report was compiled using data from Agence France-Presse and Reuters.