As Russia's special military operation in Ukraine grinds into its fourth month, officials in Kyiv have expressed fears that the specter of "war fatigue" could erode the West's resolve to help them.

The United States and its allies have given billions of dollars in weaponry to Ukraine. Europe has taken in millions of people displaced by the war.

Ukrainian President Volodymyr Zelensky has already chafed at Western suggestions that he should accept some sort of compromise, The Associated Press reported. Ukraine, he said, would decide its own terms for peace.

"The fatigue is growing, people want some kind of outcome (that is beneficial) for themselves, and we want (another) outcome for ourselves," he said.

The US was continuing to help Ukraine, with President Joe Biden saying last week that Washington will provide it with advanced weapons that will enable it to more precisely strike key targets on the battlefield. The new military aid package would include the High Mobility Artillery Rocket System, or HIMARS.

On Thursday, Konstantin Gavrilov, head of the Russian Delegation to the negotiations on military security and arms control in Vienna, told the Rossiya-24 TV channel that Moscow "particularly put the spotlight on the delivery to Ukraine of long-range howitzers and HIMARS that threaten not only Donbas but Russia as well".

"We have clearly laid out Russia's stance: If the Russian Federation is attacked with these long-range systems, a response against the decision-making centers will be immediate," he said.

According to a report by The Associated Press, Ukraine has depleted its stocks of Soviet and Russian-designed weaponry and is now completely dependent on allies for arms, US military sources say, adding that Kyiv's forces are using, or learning to use, arms wielded by the US and European NATO allies.

But, according to a US official, Washington is not willing to send Kyiv its Grey Eagle tactical drones out of fear they could be used to strike deep inside Russia, a move that could risk pulling Washington into direct conflict with Moscow.

Bucharest meeting

Kyiv has meanwhile appealed for more weapons from the West. The leaders of nine central and eastern European countries were meeting on Friday in Bucharest to plead for a strengthening of the eastern flank of NATO, ahead of a major meeting in Madrid at the end of June.

Russia has repeatedly warned the West against getting involved, with some officials warning of the risk of nuclear war.

In the frontline, intense street battles in the city of Severodonetsk in eastern Ukraine continued to rage on Friday.

Up to 100 Ukrainian soldiers were being killed every day in frontline fighting and as many as 500 wounded, Ukrainian Defense Minister Oleksiy Reznikov said.

Russia says the special military operation is meant to "de-Nazify" Ukraine.

In the southern Russian city of Volgograd－which in the Soviet era was known as Stalingrad, and was the scene of the bloodiest battle of World War II－many Russians rally behind the military operation.

"Back then there was fascism, now there is neo-fascism," said local resident Alexander Grachev, 50, referring to Ukraine's authorities.

Zelensky said earlier that Ukrainian forces were "holding on" as the fight could determine the fate of the Donbas region.

On Thursday, he signed two separate decrees imposing sanctions on Russian President Vladimir Putin and more than 200 Russian officials, including Russian Prime Minister Mikhail Mishustin and Kremlin spokesman Dmitry Peskov.