Ukraine outlined its proposal for accepting a neutral status for the country during cease-fire talks with Russia on Tuesday, demanding binding security guarantees from the U.S. and some European countries, while the five-week-old Russian war on Ukraine raged on around the country.

       The negotiations between officials from Kyiv and Moscow, held in Istanbul over the terms of a possible peace settlement, achieved no immediate breakthrough but were described as constructive by both sides.

       Meanwhile, Ukrainian President Volodymyr Zelensky escalated his criticism of Western leaders for their reluctance to tighten sanctions on Russia or provide heavier weapons for Ukraine’s defense, as delegations from Kyiv and Moscow met for cease-fire talks in Turkey.

       Mr. Zelensky, in a televised address late Monday, called for tougher sanctions, including an embargo on Russian oil sales to the European Union, to be implemented immediately rather than waiting for Moscow to step up its attacks, for example by using chemical weapons.

       “If the sanctions packages are weak or don’t work well enough, if they can be circumvented, it creates a dangerous illusion for the Russians that they can afford to continue what they are doing now," said the Ukrainian president. “And Ukrainians pay for this with their lives. Thousands of lives."

       After the talks in Istanbul, Ukrainian negotiators said that their key demands included guarantees for Ukraine’s security from the U.S., the U.K., France, Turkey, Germany, Canada, Poland and Israel.

       “This is the system we would like to build the future of Ukraine on," said Ukrainian negotiator David Arakhamia, speaking to reporters after the talks.

       “We want an international mechanism of security guarantees where guarantor countries will act in a similar way to NATO’s article number five," Mr. Arakhamia said, referring to the North Atlantic Treaty Organization’s mutual-defense promise.

       Ukrainian presidential adviser Mykhailo Podolyak said that the arrangement would be subject to a referendum of the Ukrainian people, as well as the approval of the guarantor countries.

       Mr. Podolyak said that Ukraine had offered Russia a 15-year period of negotiations on the status of Crimea, which Russia annexed by force in 2014.

       Ukrainian forces have pushed Russian troops back in areas east and northwest of Kyiv in recent days.

       Russian Deputy Defense Minister Alexander Fomin said Russia would significantly decrease its military activities around Kyiv and Chernihiv, north of the capital, in order to increase trust.

       Ukrainian officials said Russia’s statements about de-escalation could not be trusted, and that Moscow appeared to be stalling for time in order to reinforce its attacks in Ukraine’s east.

       Some Ukrainian officials have expressed guarded optimism about the prospect of a cease-fire after Russian forces failed to seize almost all of Ukraine’s major cities amid logistical problems and fierce Ukrainian resistance. Western officials say they see no sign so far that Russian President Vladimir Putin is willing to stop his assault on Ukraine, however.

       Turkish President Recep Tayyip Erdogan briefly visited the Russian and Ukrainian negotiators, who met in a former Ottoman palace on the banks of the Bosporus.

       “We are entering a period when concrete results should be achieved from negotiations," Mr. Erdogan said. “The whole world is waiting for good news from you."

       MINT PREMIUM See All

       Premium HCL Technologies eyes 10% stake in BDR Pharmaceuticals ...

       Premium Sri Lanka’s agrarian crisis a cautionary tale for India

       Premium India's space economy boom is here

       Premium Should you invest in alpha or momentum funds in India?

       Russian oligarch Roman Abramovich, who survived an alleged poisoning earlier this month, was photographed inside the room with the negotiators. Mr. Abramovich appeared to be greeting Mr. Erdogan and sitting at a table with Russian and Ukrainian officials, according to news footage reviewed by The Wall Street Journal.

       Russia’s invasion of Ukraine, which began on Feb. 24, continues unabated despite an array of financial and industrial sanctions imposed by the U.S., the EU and other, mainly advanced, economies.

       But the EU has so far rejected calls to sever its main business dealings with Russia: the purchase of oil and gas, which are Moscow’s main sources of export earnings. The U.S. banned Russian oil, gas and coal imports on March 8.

       Many observers believe public pressure on EU leaders to act could become overwhelming if Mr. Putin orders the use of chemical or other unconventional weapons in Ukraine. At an EU summit last week, some officials argued that the bloc should keep its powder dry, imposing further sanctions only in reaction to a further escalation by Russia.

       “There are simply no words. Just think about what it has come down to. Waiting for chemical weapons. We, living people, have to wait," Mr. Zelensky said in his televised address. “Doesn’t everything the Russian military has done so far deserve an oil embargo?"

       Some eastern and northern EU countries support sanctions on Russian energy imports, but Germany, Europe’s biggest economy, has steadfastly rejected an immediate cutoff of Russian oil and gas. German Chancellor Olaf Scholz on Sunday warned of devastating economic consequences for his country if it bans Russian oil, dismissing studies by economists that say the impact would be manageable.

       German officials have, however, said the country would find ways to cope if Moscow, rather than Berlin, cuts off oil and gas deliveries, raising doubts about Mr. Scholz’s claim that Germany couldn’t cope without Russian energy imports.

       Losing access to Russian gas during colder months would mean activating German emergency plans to conserve fuel for heating, including suspending some industrial activities—such as in the chemicals sector—that use gas in the production process.

       Some German politicians, such as former Finance Minister Wolfgang Sch？uble, have called for an immediate if temporary embargo on all energy purchases from Russia to destroy the economic underpinnings of Mr. Putin’s military offensive.

       Mr. Zelensky also called for more weapons, including warplanes, tanks, artillery and shells.

       “Ukrainians should not die just because someone cannot find enough courage to hand over weapons to Ukraine," he said. “Fear always makes you an accomplice."

       Ukraine’s armed forces have inflicted heavy losses on Russian troops despite expectations among Western governments that the country would quickly collapse in the face of Mr. Putin’s invasion.

       Ukraine’s defenders have received mainly lighter weapons from the U.S. and some European countries, such as shoulder-fired antitank and antiaircraft missiles. But Kyiv argues it needs heavier weapons to support its counterattacks aimed at reclaiming more territory from the invading Russians.

       Mr. Zelensky listed recent tactical victories over Russian forces, saying Ukraine’s army was pushing them back from the outskirts of Kyiv. He said Irpin, a town to Kyiv’s northwest, had been retaken, although a senior U.S. official said Monday they couldn’t independently verify the claim.

       Mr. Zelensky also called on Ukrainians to remain grounded despite recent military successes. “We can’t set expectations too high," he said, noting that Russian forces were regrouping.

       Ukrainian officials reported advances in other parts of the country. Oleksandr Vilkul, head of the military administration in Kryvyi Rih in central Ukraine, said that Ukrainian forces had repelled Russian attacks and pushed them 25 miles from the city, which is Mr. Zelensky’s hometown.

       “The main thing is that after the stress of the first days, we have realized that we can not only halt the enemy, but strike and defeat it," Mr. Vilkul said in a video address.

       A Russian cruise missile struck the regional government building in Mykolayiv in southern Ukraine on Tuesday morning, the regional governor said. Rescuers were searching the damaged building, half of which was destroyed, for eight civilians and three soldiers who were missing, while more than 50 people managed to get out, Gov. Vitaliy Kim said on the Telegram messaging app.

       Maj. Gen. Dmitro Marchenko, the head of Mykolayiv’s defense, said 15 people were missing and that 16 had been injured. Vans transported bodies to the regional morgue in the city after the strike.

       Mr. Kim said half the building was destroyed, including his office, and that he wasn’t there because he had overslept.

       Ukrainian forces have in recent days pushed Russian units back from the edge of Mykolayiv, a key city on the road to the Black Sea port of Odessa.

       —Yuliya Chernova, Marcus Walker and Bojan Pancevski contributed to this article.

       Subscribe to Mint Newsletters

       * Enter a valid email

       * Thank you for subscribing to our newsletter.

       Download the App to get 14 days of unlimited access to Mint Premium absolutely free!

       Topics russia-ukraine crisis