The UK has accused Russia of “cynical brinkmanship” over threats to collapse a deal that allows Ukraine grain to be exported to countries at risk of famine.

The Black Sea Grain Initiative is a deal negotiated with Kyiv and Moscow by Turkey and the United Nations in July 2022 to ease a global food crisis, allowing agricultural produce from the wartorn nation’s southern ports to be shipped out without fear of attack.

It came with a separate agreement with Russia to facilitate shipments of its food and fertiliser, which have been exempted from Western sanctions regimes applied since the invasion started more than 500 days ago.

The agreement has helped to lower global prices of food commodities such as wheat after they surged to record highs following Russian president Vladimir Putin’s attack last year, with grain prices spiking from 750 US dollars (£570) per bushel pre-invasion to 1,350 (£1,027) in March 2022.

The Russians are masters of this sort of brinkmanship and they absolutely don’t care whether they are playing with human life or not

The deal has been extended every three months but Moscow has signalled that it does not intend to continue the accord when it comes up for renewal for a fourth time next week.

Dame Barbara Woodward, the UK’s permanent representative to the UN in New York, told reporters: “This is a particularly tough moment because we have seen at every renewal point, including this one, that the Russian approach is simply cynical brinkmanship.

“In Istanbul, they slow roll the inspections of the grain ships, bringing down the amount of grain that goes out. Then, by signalling that they are considering refusing to renew the deal, they are also affecting global grain prices.

“Russia has claimed that they are withdrawing because their side of the deal on food and fertiliser export problems is not being upheld. That is patently untrue.

“They are actually getting more grain and fertiliser out of Novorossiysk into export markets than they were before Putin launched his war against Ukraine.”

The ambassador said that, should the deal collapse, cargo ships carrying grain out of Ukraine could be under threat of attack by the Russians.

Speaking on Thursday, she said the initiative had led to 33 million tonnes of grain and food exports leaving Ukraine, with the majority going to areas of the globe struggling with nutrition supplies.

“About 61% of that has gone to low and middle income countries, or 65% if you look at wheat alone,” Dame Barbara said.

“So almost two-thirds is going to key markets where famine is a threat or food insecurity is a threat.”

Some of the grain released from Black Sea ports has been purchased by the World Food Programme and shipped into places such as Afghanistan, Ethiopia, Somalia and Sudan — countries that Dame Barbara described as being on UN “famine watch”.

Russia insists the agreement has not worked for its own exports, blaming Western sanctions for hindering financing and insurance.

Kremlin spokesman Dmitry Peskov said: “At the moment, unfortunately, we don’t see any particular grounds for extending this deal.”

Andrew Clark, head of the Foreign Office’s Grain Cell unit, said negotiations with Moscow over previous renewals had often “gone down to the wire”.

“Nonetheless, we are increasingly pessimistic about the progress of negotiations for this renewal,” he said at a briefing.

Western sources told the PA news agency that the Kremlin was acting “more recklessly” ahead of Tuesday’s renewal deadline.

“Every 120 days we go through this and the Russians are masters of this sort of brinkmanship and they absolutely don’t care whether they are playing with human life or not,” said a source.

“I think the mood music around this is different and darker this time than it was on the previous three renewals. Russia is playing much more recklessly in terms of brinkmanship.”

One of the conditions the Kremlin has placed on signing up again is for a pipeline carrying ammonia, a key ingredient in fertiliser, between Tolyatti and Odesa to be repaired.

But Dame Barbara said the pipeline damage means it “would be impossible to bring it on-stream” and that the final stretch “runs through territory which is now part of the front line”.

There are also understood to be concerns in the West that Turkish president Recep Tayyip Erdogan might not have the same influence over Russia’s leader as he exerted last summer during the brokering of the grain deal.

Mr Putin reportedly was angered by Turkey after it freed commanders of the Ukrainian Azov Regiment that were being held under a prisoner swap deal.

Ankara had originally said the defenders of Mariupol would be kept in Turkey until the end of the war but a video released last week showed them being welcomed back to Ukraine by the country’s president, Volodymyr Zelensky.

Alternatives to shipping grain out of Ukraine involve using rail routes and canals but both modes are more expensive and can handle less cargo volume than sea vessels.