Nato Secretary-General Jens Stoltenberg has said Western countries need to "prepare for the long haul".
Speaking to reporters after meeting US President Joe Biden at the White House on Thursday, Stoltenberg said Nato must continue to support Ukraine in what was becoming a long and sustained conflict:
"We just have to be prepared for the long haul because what we see is that this war has become a war of attrition where the Ukrainians are paying a high price for defending their own country on the battlefield, but also where we see that Russia is taking high casualties.
"Our responsibility is to provide support to Ukraine. Most wars - and also most likely this war - will at some stage end at the negotiating table, but what we know is that what happens around the negotiating table is very closely linked to the situation on the ground, on the battlefield, so we need to help them, to support them, so they can achieve the best possible outcome of this conflict."
One hundred days into Russia’s invasion of Ukraine, the war has brought the world a near-daily drumbeat of gut wrenching scenes: Civilian corpses in the streets of Bucha; a blown-up theater in Mariupol; the chaos at a Kramatorsk train station in the wake of a Russian missile strike.
Nobody really knows how many combatants or civilians have died, and claims of casualties by government officials — who may sometimes be exaggerating or lowballing their figures for public relations reasons — are all but impossible to verify.
Government officials, U.N. agencies and others who carry out the grim task of counting the dead don’t always get access to places where people were killed.
Russia is now achieving "tactical success" in the eastern Donbas region of Ukraine, but it's come at a "significant resource cost", the UK's Ministry of Defence has said in its latest intelligence update.
Questions remain around Moscow's decision to concentrate so much of its "force and fires" on a single part of the overall campaign.
Looking back at the 100 days since Russia invaded its neighbour, the MoD also reminds people that Vladimir Putin's original plan - to seize the capital Kyiv and topple Ukraine's government - has failed.
However, 90% of Luhansk - part of the Donbas region - is now controlled by Russia, the update said. And it is likely Russian President Vladimir Putin will have complete control of the area in the next two weeks.
Earlier, on Thursday, Ukraine's President Volodymyr Zelensky says that Russian forces have seized 20% of his country's territory, as Moscow's invasion nears its 100th day.
Addressing lawmakers in Luxembourg, he added that the front line extended for more than 1,000km (621 miles).
"All combat-ready Russian military formations are involved in this aggression," he told MPs via videolink.
Russian forces have been intensifying attacks on the city of Severodonetsk in the eastern Donbas region.
Sievierodonetsk is currently the acting administrative center of Luhansk Oblast. By May 2022, Sievierodonetsk and its direct neighbor, the city of Lysychansk, were the only remaining Ukrainian strongholds in the otherwise occupied Luhansk Oblast.
The Institute for the Study of War (ISW) judged on May 28 that the Russian military was directing a large part of its combat-effective forces into the battle of Sievierodonetsk, weakening other front lines and risking exhausting its remaining troops.
The ISW cautioned that the effort invested in the capture of Sievierodonetsk did not seem fitting for the location's limited strategic value. A Ukrainian military analyst believes this is the last offensive Russia can undertake before Western military aid reaches Ukrainian forces. Ukrainian forces may be withdrawing to preserve their forces.
According to the UK Ministry of Defence, as of June 2, Russia had taken control of most of Sievierodonetsk.
(with inputs from agencies)
