Ukrainian Defence Minister Oleksii Reznikov has submitted his resignation in the biggest shakeup of the defence establishment in 18 months of war with Russia.
Reznikov has been at the forefront of Ukraine's lobbying for foreign weapons to fight Russia's invasion but his departure after months of corruption allegations against his ministry is not expected to have a big effect on military operations.
President Volodymyr Zelenskiy said on Sunday he was sacking Reznikov and proposed Rustem Umerov, a Crimean Tatar and ex-MP who runs the State Property Fund, to replace him.
Reznikov, who took office in 2021, has helped Ukraine secure billions of dollars worth of foreign military aid since Russia's invasion in February 2022.
Ukraine has received weapons including German battle tanks, HIMARS rocket launchers from the United States and Storm Shadow cruise missiles from the United Kingdom to push back Russian forces, and is poised to receive US F-16 fighter jets soon.
"Reznikov did an amazing job building up a relationship with other ministers and other ministries," Andriy Zagorodnyuk, defence minister from 2019-20, told Reuters.
"It saved the country because he was the owner of the process of arranging the shipments of weapons and so on."
Reznikov, a 57-year-old former lawyer, was not implicated personally by corruption allegations levelled by Ukrainian media at the defence ministry, most notably over procurement.
But the accusations prompted calls for him to be fired and Reznikov portrayed himself as the victim of a smear campaign
In his resignation letter, Reznikov provided an overview of his 22 months in the post, praising Ukraine's fierce wartime resistance against Russian forces and his ministry's lobbying efforts for military aid.
"Over 50 per cent of the temporarily occupied territories by Russia have already been liberated. Every day our defenders are moving forward," he said in the letter, posted on X.
"There is an understanding that Ukraine is a shield of Europe in the east."
Reznikov, who has been tipped to become Ukraine's ambassador to London, said he saw one of Ukraine's priorities as building long-term partnerships with allies and securing "real security guarantees".
Umerov's candidacy is due to be reviewed by parliament later this week.
Meanwhile,Turkish President Tayyip Erdogan said after talks with his Russian counterpart Vladimir Putin on Monday that it would soon be possible to revive the grain deal that the United Nations says helped to ease a food crisis by getting Ukrainian grain to market.
Russia quit the deal in July - a year after it was brokered by the United Nations and Turkey - complaining that its own food and fertiliser exports faced serious obstacles.
Erdogan, who previously played a significant role in convincing Putin to stick with the deal, and the UN are both trying to get Putin to return to the deal.
"As Turkey, we believe that we will reach a solution that will meet the expectations in a short time," Erdogan said in the Black Sea resort of Sochi after his first face to face meeting with Putin since 2022.
Erdogan said that Russia's expectations were well-known to all and that the shortcomings should be eliminated, adding that Turkey and the UN had worked on a new package of suggestions to ease Russian concerns.
Putin has said Russia could return to the grain deal if the US and European countries fulfil a separate memorandum agreed with the UN at the same time to facilitate Russian food and fertiliser exports.
Standing beside Erdogan, Putin said Russia could return to the deal but only if Russian agricultural exports were no longer restricted from reaching global markets.
"We will be ready to consider the possibility of reviving the grain deal and I told Mr President about this again today - we will do this as soon as all the agreements on lifting restrictions on the export of Russian agricultural products are fully implemented," Putin said.