KYIV: Russia halted participation on Monday in the year-old U.N.-brokered deal that lets Ukraine export grain through the Black Sea, causing concern in poorer countries that price rises will put food out of reach.

Hours earlier, a blast knocked out Russia's bridge to Crimea in what Moscow called a strike by Ukrainian sea drones, killing two people. Moscow said it was a terrorist attack on the road bridge, a major artery for Russian troops fighting in Ukraine.

The Kremlin said there was no link between the attack and its decision to suspend the grain deal, over what it called a failure to meet its demands to implement a parallel agreement easing rules for its own food and fertilizer exports.

"Unfortunately, the part of these Black Sea agreements concerning Russia has not been implemented so far, so its effect is terminated," Kremlin spokesman Dmitry Peskov told reporters.

U.N. Secretary-General Antonio Guterres signalled that Russia's withdrawal meant that the related pact to assist Russia's grain and fertilizer exports was also terminated.

"Today's decision by the Russian Federation will strike a blow to people in need everywhere," he told reporters.

Moscow said it would consider rejoining the grain deal if it saw "concrete results" on its demands but that its guarantees for the safety of navigation would meanwhile be revoked.

In Washington, the White House said Russia's suspension of the pact "will worsen food security and harm millions" and U.S. Secretary of State Antony Blinken called it unconscionable.

IMPACT COULD BE PROFOUND IN AFRICA

Ukraine and Russia are some of the world's biggest exporters of grain and other foodstuffs and any interruption could drive up food prices across the globe.

Shashwat Saraf, the emergency director in East Africa for the International Rescue Committee (IRC), said the impact would be profound in Somalia, Ethiopia and Kenya, which have been facing the Horn of Africa's worst drought in decades.

"I don't know how we will survive," said Halima Hussein, a mother of five living in a crowded camp in Somalia's capital Mogadishu for people displaced by years of failed rains and violence.

Ukraine's President Volodymyr Zelenskiy raised the prospect of resuming grain exports without Russia's participation, suggesting Kyiv would seek Turkey's support to effectively negate the Russian de facto blockade imposed last year.

"Ukraine, the U.N. and Turkey together can ensure the operation of a food corridor and vessel inspections, Zelenskiy said in his nightly video message, saying said the world "has the opportunity to show that blackmail is not allowed ... We must all ensure security, protection from Russian madness."

RUSSIAN OFFENSIVE

Ukrainian forces have been striking Russian supply lines as it pursues a counteroffensive to drive Russian forces out of its south and east. On Monday it reported two more civilians killed by Russian forces, which it said had begun a major push in the northeast.

"For two days running, the enemy has been actively on the offensive in the Kupiansk sector in Kharkiv region. We are defending. Heavy fighting is going on and the positions of both sides change dynamically several times a day," Deputy Defence Minister Hanna Maliar, wrote on Telegram.

The armed forces said Russia had amassed a huge array of forces.

"In the Lyman-Kupiansk sector the enemy has concentrated a very powerful grouping. More than 100,000 personnel, more than 900 tanks, more than 555 artillery systems, and 370 multiple launch rocket systems," Serhiy Cherevatyi, spokesperson for the Ukrainian Armed Forces East group, said on national TV.

Reuters was not able to verify the accounts and there was no immediate comment from Russia.

The blast on the road bridge to Crimea could limit Moscow's ability to supply its troops in southern Ukraine, although Russian President Vladimir Putin said the bridge had not been used for military transports for a long time. Partial road traffic had been restored, Russian Deputy Prime Minister Marat Khusnullin said on Telegram.

Earlier, images showed part of the road bridge had come down and traffic halted in both directions, although a parallel railway bridge was still operational. Blasts were reported before dawn on the 19-km (12-mile) bridge, which Putin ordered built after seizing and annexing Crimea from Ukraine in 2014.

Putin told officials Russia would respond to the "senseless" attack.

Ukrainian media quoted unidentified officials as saying Ukraine's Security Service (SBU) had deployed maritime drones against the bridge. SBU spokesperson Artem Dekhtyarenko alluded to the idea that the agency would reveal details after Ukraine won the war, without directly claiming responsibility.

Ukraine says the bridge is illegal. It was hit by a massive explosion and fire in October.

The grain deal was hailed as preventing a global food emergency when brokered by the United Nations and Turkey last year.

Global commodity food prices rose on Monday, though the increase was limited, suggesting traders did not yet anticipate a severe supply crisis.

Western countries say Russia is trying to use its leverage over the grain deal to weaken financial sanctions, which do not apply to Russia's agricultural exports.

Russia has extended the Black Sea deal three times, despite repeated threats to quit. It suspended participation after an attack on its fleet by seaborne Ukrainian drones in October, leading to a few days when Ukraine, Turkey and the United Nations kept exports going without Moscow.

Any resumption of shipments without Russia's blessing would probably depend on insurers. Industry sources told Reuters they were studying whether to freeze their coverage.

"The (key) question is whether Russia mines the area which would effectively cease any form of cover being offered," one insurance industry source said.