Ukraine said it was hoping that the first face-to-face peace talks with Russia in over two weeks, set for Tuesday, could lead to a ceasefire, but a U.S. official said President Vladimir Putin did not appear ready to make compromises to end the war.
The more than month-long invasion, the biggest of a Western nation since World War Two, has seen over 3.8 million people flee abroad, left thousands dead or injured, and brought the isolation of Russia's economy.
Nearly 5,000 people have been killed, including about 210 children, in the port city of Mariupol amid heavy Russian bombardment, according to figures from the mayor. Reuters was unable to immediately verify the numbers.
Survivors have told harrowing tales of people dying from lack of medical treatment, bodies being buried wherever space could be found, and women giving birth in basements.
A Ukrainian delegation arrived in Istanbul for the negotiations, TV footage showed.
"The minimum programme will be humanitarian questions, and the maximum programme is reaching an agreement on a ceasefire," Ukrainian foreign minister Dmytro Kuleba said on national television.
"We are not trading people, land or sovereignty."
Putin does not appear ready to make compromises to end the war, a senior U.S. State Department official told Reuters on Monday on condition of anonymity.
And Ukrainian interior ministry adviser Vadym Denysenko said earlier that he doubted "there will be any breakthrough on the main issues."
Kremlin spokesperson Dmitry Peskov said talks so far had not yielded any substantial breakthroughs but that it was important that they continued in person. He declined to give more information, saying that to do so could interfere with the process.
In besieged Ukrainian cities where conditions are desperate, the threat of Russian attacks blocked exit routes for civilians, two Ukrainian officials said.
In Mariupol, the mayor said some 160,000 people are trapped.
"There is no food for the children, especially the infants. They delivered babies in basements because women had nowhere to go to give birth, all the maternity hospitals were destroyed," a grocery worker from Mariupol who gave her name only as Nataliia told Reuters after reaching nearby Zaporizhzhia.
The United Nations said it had been able to bring food and medical supplies into Kharkiv, Ukraine's second-biggest city and one of its hardest hit.
