Defence minister Rustem Umerov said Ukraine had agreed to “ensure safe navigation, eliminate the use of force, and prevent the use of commercial vessels for military purposes”.
However, Russia claimed it depended on Western sanctions being lifted on fertiliser and food companies and ensuring its access to the SWIFT payments system.
President Zelenskyy said he believed the truce was effective immediately and accused Moscow of playing games.
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“Unfortunately, even now, even today, on the very day of negotiations, we see how the Russians have already begun to manipulate,” he said.
“They are already trying to distort agreements and, in fact, deceive both our intermediaries and the entire world.”
Image: Mr Zelenskyy said Russia was already manipulating over the deal. Pic: Reuters
A White House statement said the US would help “restore Russia’s access to the world market for agricultural and fertiliser exports”.
President Trump said his administration was “looking into” Russia’s request to lift sanctions.
A senior official in the Ukrainian government, speaking anonymously to the AP news agency, said Kyiv did not agree to lifting sanctions as a condition for a maritime ceasefire.
They said Russia had done nothing to have sanctions reversed.
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Child killed in Russian drone strike on Kyiv
While uncertainty remains over the terms of the Black Sea truce, the Kremlin confirmed it would honour a ceasefire on attacking energy facilities until 17 April.
It said oil refineries, pipelines, power plants and substations, nuclear power plants and hydroelectric dams were all covered by the deal.
It added: “In the event of a violation of the moratorium by one of the parties, the other party has the right to consider itself free from obligations to comply with it.”
Sky News security analyst Michael Clarke said the Black Sea deal was something the US “can boast about” but won’t massively change anything on the ground in Ukraine.
“The Russians will be quite happy about that because they’ll just keep going down more and more rabbit holes,” he said.
“Unless the Americans are prepared to pressure Russia as opposed to just keeping offering them more advantages, the war will just go on,” added Professor Clarke.
Earlier in March, President Zelenskyy said he was ready for a 30-day ceasefire that would also include “the entire front line”.
American secretary of state Marco Rubio said the ball was “in Russia’s court” but President Putin has declined to follow suit and named multiple pre-conditions.