Kyiv and Moscow signed a deal on Friday to free up Ukrainian grain exports that have been blocked since February.
The proposal marks the first major agreement between the two warring sides and has boosted hopes that a worsening food security crisis can now be eased.
Russian Defense Minister Sergei Shoigu and Ukrainian Infrastructure Minister Oleksandr Kubrakov signed separate but identical "mirror" deals with Turkish Defense Minister Hulusi Akar and UN Secretary-General Antonio Guterres.
"Today, there is a beacon on the Black Sea,'' Guterres said. "A beacon of hope, a beacon of possibility, a beacon of relief in a world that needs it more than ever."
What do we know about the deal?
Full details of the plan, which Turkey and United Nations chief Guterres have been working on for months, were not immediately released.
It is expected that some 22 million tonnes worth of Ukrainian grain currently stuck in silos, will now be released onto the global market. Turkish President Erdogan said that "in the coming days, we will inaugurate a new corridor from the Black Sea to many countries of the world."
Guterres said that commercial food exports will be restarted from the three Black Sea ports of Odesa, Chernomorsk and Yuzhny.
Shoigu said that Russia "will not take advantage of the fact that the ports will be cleared and opened. We have made this commitment."
Reuters cited two UN officials who said that exports should reach their pre-war levels of 5 million tonnes a month in a few weeks.
Reports suggest that the parties have agreed that ships bound for Ukraine will first be searched to ensure no weapons or other military equipment are on board.
Searches will also take place when ships carrying grain from Ukrainian ports want to move in the other direction through the Bosphorus Strait.
A coordination center would be established in Istanbul and would include UN, Turkish, Russian and Ukrainian officials.
How have world leaders reacted to the deal?
The agreement will "bring relief for developing countries on the edge of bankruptcy and the most vulnerable people on the edge of famine," UN chief Guterres said.
"It will help stabilize global food prices which were already at record levels even before the war — a true nightmare for developing countries," he added.
The EU welcomed the deal in a statement, calling it a "critical step forward in efforts to overcome the global food insecurity caused by Russia's aggression against Ukraine" adding that its success "will depend on the swift and good faith implementation of today’s agreement."
"This joint step we are taking with Ukraine and Russia will hopefully revive the path to peace," Turkish President Recep Tayyip Erdogan, who also witnessed the signing, said.
What has Ukraine said about the deal?
Ukrainian presidential advisor, Mykhailo Podolyak, wrote on Twitter on Friday that Ukraine would not sign a deal directly with Russia, but that the two would sign "mirror agreements" with Turkey and the UN.
Podolyak also said that Russian ships could not escort the grain vessels nor could Russia have any presence in Ukrainian ports.
"All inspectors of transport ships will be carried out by joint groups in Turkish waters in the event of such a need," he added.
Kyiv has also sought guarantees that Russia won't use the safe shipping corridors created by the deal to attack the Black Sea port of Odesa.
The United States has cautiously welcomed the deal. US State Department spokesperson Ned Price said Washington would focus on holding Moscow accountable for keeping to the terms of the agreement.
How has food security been impacted by the blockade?
Since the conflict began, up to 25 million tons of wheat and other grain have been held up by Russian warships in Ukrainian ports.
Kyiv, meanwhile laid landmines in its waters to avert a feared amphibious assault, which has further hampered exports by sea.
Ukraine has also accused Russia of stealing grain from its eastern regions to sell, and deliberately shelling Ukrainian fields to set them on fire.
Although some of the grain is being transported through Europe by rail, road and river, the amount is small compared with sea routes.
Several parts of the Middle East and Africa now face serious food shortages.
Russia has denied responsibility for worsening food security. Instead, Moscow has blamed Western sanctions for slowing its own food and fertilizer exports.
The signing of the deal comes a day after Russia restored critical gas supplies to Europe via Germany, easing fears of an energy crisis this winter.
The Nord Stream 1 gas pipeline had been shut for 10 days of maintenance, stoking fears it might not be turned on again.
However, while it did come back online, the gas being sent through was only at 40% capacity.
ab, mm/wmr (AP, AFP, dpa, Reuters)