"The Black Sea Grain Initiative will be prolonged for 120 days," Ukrainian Infrastructure Minister Oleksandr Kubrakov said on Twitter, while a senior Turkish official confirmed to AFP that the deal had been extended "under current terms."
Turkish President Recep Tayyip Erdogan tweeted: "It has been clearly seen how important and beneficial this agreement is for the food supply and security of the world."
Since July, some 11.1 million tons of agricultural products have been shipped under the grain deal, including 4.5 million tons of corn and 3.2 million tons of wheat.
UN Secretary General Antonio Guterres hailed the extension and said "I welcome the agreement by all parties to continue the Black Sea grain initiative to facilitate the safe navigation of export of grain, foodstuffs and fertilizers from Ukraine," UN Secretary General Antonio Guterres said in a statement on Thursday.
Extending the grain deal "continues to demonstrate the importance of discreet diplomacy in the context of finding multilateral solutions," he said.
Guterres said the UN was also "fully committed to removing the remaining obstacles to exporting food and fertilizers from the Russian Federation" - a part of the deal Moscow sees as critical.
The export of Russian ammonia via a pipeline to the Black Sea has not yet been agreed as part of the renewal, a source familiar with discussions told Reuters.
Both agreements were "essential to bring down the prices of food and fertiliser and avoid a global food crisis," Guterres said in a statement released by the Istanbul-based Joint Coordination Center (JCC) that has been overseeing the agreement.
The flow of Ukrainian exports is essential to stabilizing prices on international markets and to supplying the populations most vulnerable to the risk of hunger, particularly in Africa.
Some 40 percent of the grain exported under the agreement has gone to developing countries. It has been especially critical for East African nations such as Ethiopia which have suffered growing hunger in the face of relentless drought.
Russia's invasion blocked 20 million tons of grain in Ukraine's ports before the United Nations and Turkey brokered the deal in July.
In the weeks of intense diplomacy leading up to Thursday's announcement, much of the negotiations focused on the issue of fertilizers, a UN source said on condition of anonymity.
Agricultural products and fertilizers do not fall under the sanctions against Russia but because of the risks in the Black Sea linked to the Ukraine conflict, it has become difficult to insure the vessels transporting them.
According to the UN source, a policy framework has been established for the exceptions in insurance, access to ports, financial transactions, shipping and access for shipping, in compliance with the sanctions imposed on Russia.
This report was prepared using data from Agence France-Presse and Reuters.