António Guterres, the United Nations secretary general, is scheduled to arrive on Friday in Odesa, Ukraine's largest port city, in the midst of a war that has underscored the limits of his organization's influence when one of its most powerful members instigates a war.
A day after meeting with President Volodymyr Zelensky of Ukraine and President Recep Tayyip Erdogan of Turkey in Lviv, in western Ukraine, Mr. Guterres will witness the progress of one of the U.N.'s most concrete recent achievements: grain shipments leaving Ukraine for global markets.
The shipments are the product of a fragile agreement brokered by the U.N. and Turkey to restore the flow of grain from Ukraine, one of the world's breadbaskets, and facilitate exports of Russian grain and fertilizer that Moscow says have been hindered by international sanctions on banking and shipping. The monthslong absence of so much grain aggravated a global food crisis, stoked famine in Africa and contributed to soaring grain prices.
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On Thursday, Mr. Guterres heralded the effectiveness of the deal, saying it confirmed the U.N.'s vital role as a mediator.
"The positive momentum on the food front reflects a victory for diplomacy - for multilateralism," said Mr. Guterres, a former Portuguese prime minister.
But he also acknowledged that the unresolved problem that had brought him to Ukraine was the war. As the head of a global organization whose charter pledges to end "the scourge of war," Mr. Guterres has repeatedly called for a political solution to end the conflict and has offered to mediate, to little avail.
As an example of the obstacles the U.N. leader has faced, from the beginning of Russia's invasion in late February until April, Mr. Guterres could not get President Vladimir V. Putin of Russia on the phone, according to his spokesman, Stéphane Dujarric.
An urgent issue the U.N. faces in Ukraine is the increasingly dangerous situation at the Zaporizhzhia Nuclear Power Plant, a Russian-occupied complex that has spawned fears of a radiation disaster because of persistent shelling, and now tit-for-tat accusations of preparations for an outright attack. The U.N. nuclear watchdog, the International Atomic Energy Agency, needs the agreement of both sides to send inspectors into the plant.
Mr. Guterres said on Thursday that a failure to prevent damage at the plant would amount to "suicide."
Some of the most effective efforts to punish Russia have come in the form of tough economic sanctions imposed by the United States and the European Union, but those came outside the Security Council, the structure within the U.N. that has the power to impose sanctions.
While the war has laid bare the limits of the U.N.'s ability to resolve global conflicts, it has also showcased the organization's vital humanitarian role, providing aid, food and health care to millions of Ukrainian refugees. Mr. Guterres himself served as the U.N. High Commissioner for Refugees from June 2005 to December 2015, taking up the role of secretary general in 2017.
The Ukraine conflict has unleashed a devastating humanitarian toll. Uncounted thousands of civilians have been killed, millions are internally displaced and more than six million are now living outside of the country, in what the U.N. has called the fastest-growing refugee crisis since World War II. Russia's targeting of civilians and treatment of captured enemy fighters has also led to accusations of war crimes.
But Russia holds veto power on the Security Council, robbing it of the ability to pass legally binding resolutions holding Moscow accountable. And Russia has a powerful ally, with its own veto, on the council: China.
The Ukraine war is hardly the first conflict in which the Security Council has been rendered impotent by the competing aims of its five permanent, veto-wielding members: Russia, China, the United States, Britain and France.
Among the council's most striking recent failures is the yearslong civil war in Syria, in which Russia blocked definitive action. China's and Russia's alliances kept the Security Council from moving aggressively to counter atrocities against the Rohingya ethnic group in Myanmar. North Korea, which China also protects, has repeatedly ignored U.N. prohibitions against conducting nuclear tests.
Cases where the council was able to act include imposing painful sanctions on Iran over its nuclear program. The council also authorized military intervention in support of Libyan rebels in 2011, despite Russia's reluctance - but the assassination of the Libyan dictator, Muammar Qaddafi, reinforced Russian suspicion of the organization.