The foreign ministers of Russia and Ukraine are to hold talks in Turkey, as Moscow's all-out invasion of its neighbour enters its third week.
Ukraine's Dmytro Kuleba said ahead of the face-to-face meeting with his Russian counterpart Sergei Lavrov that his expectations were "limited".
It comes after Ukraine accused Russia of bombing a children's hospital - an attack Kyiv says is a "war crime".
Ukraine says 17 people were hurt in the attack in Mariupol on Wednesday.
Footage has since emerged showing a building - which also housed a maternity ward - reduced to a shell, with a huge crater nearby.
The bombing has been widely condemned, with the UN Secretary General António Guterres describing the attack as "horrific", and the US accusing Russia of a "barbaric use of military force to go after innocent civilians".
But Russia's deputy ambassador to the UN, Dmitry Polyanskiy, said the bombed hospital had been "turned into a military object by [Ukrainian] radicals".
Mariupol - where about 400,000 people live - has been surrounded by Russian forces for several days, and repeated attempts at a ceasefire to allow civilians to leave have broken down.
"The whole city remains without electricity, water, food, whatever and people are dying because of dehydration," Olena Stokoz of Ukraine's Red Cross told the BBC on Wednesday.
Russian warplanes also hit residential areas in overnight raids in Ukraine's north-eastern Sumy region, local officials said.
Ahead of Thursday's talks in Antalya, southern Turkey, Mr Kuleba said: "Frankly... my expectations of the talks are low."
Ukraine's foreign ministry said that Kyiv was seeking an immediate "cessation of hostilities and the war against Ukraine by Russia".
Meanwhile, Russia is demanding that Ukraine abandons its stated plans to join the Nato military alliance, and becomes a neutral-status state. It also says Kyiv must accept Moscow's jurisdiction over Crimea - the southern Ukrainian peninsula annexed by Russia in 2014.
And Russia is pressing for Kyiv to recognise two self-proclaimed rebel regions in eastern Ukraine.
Two previous rounds of talks held in recent days failed to find any breakthrough, although the two warring sides agreed on establishing humanitarian corridors to help evacuate civilians from several besieged cities.
Ukraine said it expected more civilians would be allowed to leave cities besieged by Russian troops later on Thursday.
In the aftermath of the hospital bombing, a flurry of telephone diplomacy took place.
The UK's Prime Minister had a call with Ukraine's President Zelensky on Wednesday evening, in which he condemned the attack and "committed to further tighten... sanctions", according to Downing Street notes on the call. Ukraine's ambassador to the UK, however, has called for that country to end "bureaucratic red tape" for refugees attempting to flee the war.
The United States Secretary of State Antony Blinken, meanwhile, spoke with his counterpart Mr Kuleba about "unconscionable attacks harming population centres", the US State Department said. It comes as US Vice-President Kamala Harris is in Poland, a day after Washington rejected the country's plan to transfer its jet fleet to the US, rather than directly to Ukraine.
Soon after, the United States House of Representatives voted in favour of nearly $14bn (£10.6bn) in aid for Ukraine, as well as voting to ban US imports of Russian oil and other energy products. The measures still must pass through the Senate, which is expected to vote later this week.
Western officials - including the White House - have also warned Russia could use chemical or biological weapons in Ukraine or create a "false flag" operation - a misleading operation blamed on the other side, usually used to justify a supposed counter-attack. Moscow earlier said Ukrainian forces had transported some 80 tonnes of ammonia in the country's north-east, without providing evidence.
And in Europe, EU leaders are meeting in France's Palace of Versailles for a two-day summit to discuss Ukraine's possible future membership, more sanctions on Russia, and a new common defence policy.
US officials estimated that between 5,000 to 6,000 Russian troops have been killed in Ukraine since the war began on 24 February.
Ukraine says more than 12,000 Russian service personnel have died, while Russia last week acknowledged 498 fatalities - but none of the competing claims can be clearly verified.