Zelensky Says He’ll Replace Oleksii Reznikov as Ukraine’s Defense Minister

President Volodymyr Zelensky said on Sunday that he was replacing his minister of defense, the biggest shake-up in the leadership of Ukraine’s war effort since Russia’s full-scale invasion began, citing the need for “new approaches” after more than 18 months of conflict.

The fate of the defense minister, Oleksii Reznikov, had been the subject of increasing speculation in Ukraine as financial improprieties in the ministry came to light and the government started several investigations into official corruption.

Mr. Zelensky said in a statement that Mr. Reznikov, who has not been personally implicated in the widening investigations into mishandling of military contracts, would be replaced by Rustem Umerov, the chairman of Ukraine’s State Property Fund. Mr. Zelensky said he expected Ukraine’s Parliament, which must approve the change, to sign off on his request.

“Oleksii Reznikov has gone through more than 550 days of full-scale war,” Mr. Zelensky said in a statement announcing his decision on Sunday night. “I believe that the ministry needs new approaches and other formats of interaction with both the military and society at large.”

The decision to replace Mr. Reznikov atop the Defense Ministry comes as Ukraine is in the midst of a major counteroffensive, slowly gaining territory in the south and the east. Last week, Ukrainian officials said they had captured the southern village of Robotyne, suggesting that the offensive had penetrated the first layer of minefields, tank traps, trenches and bunkers Moscow has deployed between Ukraine’s forces and Russian-occupied Crimea.

The shake-up arose from several factors, according to an official in the president’s office, who was not authorized to speak publicly about the dismissal. Those included an understanding that Ukraine will need new leadership as the war drags on, the din of criticism from Ukrainian civil society groups and media over the contracting scandals, and Mr. Reznikov’s own requests to step down.

Though a member of an opposition political party, Mr. Umerov, a former investment banker, has taken on several critical roles for the Zelensky government since the war began. He was the chief Ukrainian negotiator of the Black Sea Grain Initiative and a prominent negotiator on prisoner exchanges.

He is a Crimean Tatar, a member of the ethnic group persecuted under Russia’s occupation of the Crimean Peninsula.

On Monday morning Mr. Reznikov, who has repeatedly faced questions about his future in recent weeks, including about whether he would move to a diplomatic role as ambassador to Britain, said he had submitted his letter of resignation to the chairman of Ukraine’s Parliament.

“It was an honor to serve the Ukrainian people and work for the #UAarmy for the last 22 months, the toughest period of Ukraine’s modern history,” he wrote on social media, without mentioning a new assignment.

Since the start of the war, Mr. Reznikov has become a public face for Ukraine on the world stage. He was among a handful of Mr. Zelensky’s top security officials who remained in Kyiv, the capital, as it was partially surrounded by Russian forces after the start of the invasion in February 2022.

The decision to replace Mr. Reznikov notwithstanding, Ukraine has experienced far more stability over the course of the invasion than Russia.

Moscow has undergone several military leadership changes amid criticism of its battlefield tactics, and in June, there was a brief rebellion by the mercenary leader Yevgeny V. Prigozhin, who marched members of his Wagner private military company toward Moscow. He was declared dead after a fiery plane crash last month that some Western officials have suggested had been orchestrated by President Vladimir V. Putin.

In October 2022, the Kremlin appointed Gen. Sergei Surovikin to command its forces in Ukraine. He lasted just three months before he was replaced by Gen. Valery V. Gerasimov, Russia’s highest-ranking military officer. U.S. officials have said General Surovikin had advance knowledge of the rebellion plans of Mr. Prigozhin.

Mr. Reznikov had won praise for negotiating the transfer of vast quantities of donated Western weaponry, and he oversaw the expansion of the army and its transition from an arsenal of Soviet-legacy armaments to Western systems even as his country was under attack.

In the first month of the war, Ukraine’s army rebuffed Russia’s invasion with foreign military assistance limited mostly to shoulder-fired anti-tank weapons, but it has since incorporated a wide-ranging arsenal of Western heavy weaponry. In its counteroffensive in the Zaporizhzhia and Donetsk regions in the country’s south, Ukraine has relied on U.S. and European armored vehicles, tanks, artillery and guided rockets.

But the Ministry of Defense has been buffeted this year by a string of allegations of mishandling military contracting and corruption as its budget ballooned. At one point, $986 million worth of weaponry the ministry had contracted for was undelivered by dates specified in contracts, according to government figures. Some deliveries are months late.

Ukrainian investigative journalists have found other woes with military contracting, seeming to show huge overpayments for basic supplies for the army such as eggs, canned beans and winter coats.

Mr. Reznikov had said the ministry was suing to recoup money lost in the weapons contracts. Government officials have said many of the problems had arisen in the early, chaotic days of the war in Ukraine’s frantic scramble to buy weapons and ammunition and have since been fixed. Two ministry officials — a deputy minister and head of procurement — were arrested over the winter after the reports of overpriced eggs.

With some U.S. critics of the war citing graft as an argument for limiting military aid to Ukraine, the White House national security adviser, Jake Sullivan, last week met with three high-ranking Ukrainian officials to discuss efforts to stamp out wartime corruption.

The contracting scandals prompted some calls for Mr. Reznikov’s resignation, but it appears that the change was not anticipated in Washington.

As of Friday, Mr. Reznikov was scheduled to visit the Pentagon later this week to meet with Defense Secretary Lloyd J. Austin III. The two men had regular contact and spoke “relatively frequently,” according to a U.S. official who spoke on background as the news was breaking on Sunday. It is believed that they last met in person at the NATO summit in Vilnius, Lithuania, in July.

Corruption has plagued Ukraine for most of its post-independence history, but the situation improved over the past decade, according to assessments by Transparency International, a global anti-corruption group. Mr. Zelensky campaigned on an anti-corruption platform before winning the presidency in 2019, and efforts to fight graft have been widely acknowledged as crucial to Ukraine’s efforts to move closer to its Western allies, including its hopes of joining the European Union.

In recent weeks, Mr. Zelensky has stepped up measures against wartime graft, firing all the country’s recruitment officers after bribery scandals and proposing a law that would punish corruption as treason under martial law.

In May, the head of Ukraine’s Supreme Court was detained in a bribery investigation. And on Friday, Ukrainian media reported that and a court set bail at more than $25,000 for a former deputy minister of economy accused of embezzling humanitarian aid.

The allegations dogging the ministry are not related to Western weapons transfers but to domestic weapons procurement, which is not directly financed by aid from allies. These countries transfer weapons and ammunition directly to the Ukrainian army, while financial aid is directed to nonmilitary spending. Ukrainian tax revenues fund defense procurement, where the accusations of mismanagement arose.

In an earlier shake-up last summer, Mr. Zelensky dismissed the director of his domestic intelligence agency and prosecutor general, also in the wake of allegations of corruption and mismanagement.

Carol Rosenberg and Daniel Victor contributed reporting.