Ukraine said its top objective at the first face-to-face talks with Russia in over two weeks, due to take place in Turkey on Tuesday, is to secure a ceasefire, although both it and the United States were skeptical of a major breakthrough.
The more than month-long invasion, the biggest attack on a European nation since World War Two, has seen over 3.8 million people flee abroad, left thousands dead or injured, and has brought isolation to Russia's economy and tumult to markets.
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."
Russian President Vladimir 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 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.
Ukrainian President Volodymyr Zelenskiy during a Monday night address repeated calls for the West to go further in punishing Moscow for its invasion.
"We, people who are alive, have to wait. Doesn't everything the Russia military has done to date warrant an oil embargo?"
While Western countries have imposed a series of hard-hitting sanctions upon Moscow, Europe is heavily reliant on energy imports from Russia and has been so far reluctant to act to block them.
U.S. and German government officials are due to meet in Berlin this week with energy industry executives to discuss ways to boost alternative supplies for Germany.
The Kremlin has demanded that what it deems "unfriendly" countries pay for Russian gas in roubles, not euros, but is trying to decide a mechanism by which that could work.
In besieged Ukrainian cities where conditions are desperate, the threat of Russian attacks has blocked exit routes for civilians, two Ukrainian officials said.
Zelenskiy said that although Ukrainian forces have regained control over some areas in the Kyiv region, the fighting was ongoing. "Russian troops keep controlling the north of the Kyiv region," he 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.
As the humanitarian toll continues to rise, 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.
Volunteers there were helping distribute aid to residents.
"We are here to make sure that not a single person is hungry or dies of starvation," Sergey, who did not give his surname, told Reuters.
Russia calls its actions in Ukraine a "special military operation" to disarm and "denazify" its neighbour. Ukraine and the West say Putin launched an unprovoked war of aggression.
'CHANGING THEIR GOALS'
Tuesday's talks between Ukraine and Russia will be the first in person since an acrimonious meeting between foreign ministers on March 10, a sign of shifts behind the scenes as Russia's invasion has stalled and sanctions have hit home.
"We have destroyed the myth of the invincible Russian army. We are resisting against the aggression of one of the strongest armies in the world and have succeeded in making them change their goals," Kyiv Mayor Vitali Klitschko said.
He said 100 people had been killed in the capital, including four children, and 82 multi-storey buildings had been destroyed. It was not possible to verify the figures.
Russia's military signalled last week it would concentrate on expanding territory held by separatists in eastern Ukraine, but Ukraine said it saw no sign Russia had given up a plan to surround the capital.
When the sides last met in person, Ukraine accused Russian Foreign Minister Sergei Lavrov of ignoring pleas to discuss a ceasefire, while Lavrov said a halt to fighting was not even on the agenda.
Since then, they have held talks via video link and publicly discussed a formula under which Ukraine might accept some kind of formal neutral status.But neither side has budged over Russia's territorial demands, including Crimea, which Moscow seized and annexed in 2014, and eastern territories known as the Donbas, which Moscow demands Kyiv cede to separatists.