Top allies of President Vladimir Putin said Tuesday that Moscow was ready for a prolonged conflict in Ukraine in order to achieve the Kremlin's goals in the pro-Western country.

The hostilities, which entered their fourth month Tuesday, have killed thousands of people, displaced more than eight million and forced more than six million refugees to flee across the borders.

"We will continue the special military operation until all the objectives have been achieved, regardless of the massive Western aid to the Kyiv regime and the sanctions against Russia," Defence Minister Sergei Shoigu told regional counterparts from the Russia-led Collective Security Treaty Organization.

He added that Moscow's efforts to avoid civilian casualties "are of course slowing down the pace of the offensive, but this is deliberate".

Separately, the secretary of Russia's Security Council, Nikolai Patrushev, said that Moscow's offensive would last as long as necessary.

"We are not rushing to meet deadlines," Patrushev told the Russian newspaper Argumenty i Fakty in an interview published on Tuesday.

"All the goals set by the President of Russia will be fulfilled," Patrushev added.

"It cannot be otherwise, because the truth, including historical truth, is on our side."

Putin sent troops to Ukraine to "de-militarise" and "de-nazify" pro-Western Ukraine.

Russia is believed to have suffered significant human and material losses in Ukraine even though precise details have not been revealed by the Kremlin.

Western support has helped Ukraine hold off its neighbour's advances in many areas, including the capital Kyiv. Russia is now focused on securing and expanding its gains in Donbas and the southern coast.

In Kharkiv's Gorky Park, a war crimes investigation
Kharkiv, Ukraine (AFP) May 24, 2022 –

Ukrainian prosecutor Roman Petrenko inspects the remains of Russian rockets that fell on the popular Gorky Park in the country's second city Kharkiv.

Petrenko, a prosecutor from the city's Shevchenkivsky district, is wearing a gilet with "War Crimes. Kharkiv" written in large white letters.

Kharkiv's peaceful Gorky Park is full of winding alleys and has a small amusement park, with pavilions and a Ferris wheel. It is reputed to be one of the best parks in Ukraine.

Gorky Park was hit by around 50 shells in three months of war.

Prosecutors took up the case to ensure that the park could be open without the public being at risk and, above all, determine whether the attacks constitute a war crime.

Even if there were no victims, "hitting civilian targets, civilian infrastructure, trying to kill civilians and destroy cultural heritage, are considered war crimes", Petrenko said.

"An error can happen once or twice, but there are 56 hits recorded," he said.

"It's not an accident. They were targeting the park."

With a team of deminers, assistants, ushers and workers, the prosecutor notes down each crater.

He has the ammunition dug up after an inspection by deminers, then photographs it, writes it down and determines the angle of fire and the origin of the weapon.

The shells also hit a small theatre and a closed restaurant in the park.

The shrapnel even reached and damaged bronze sculptures of children scattered around the park.

A duo of American deminers from the Bombs Tech Without Borders advise their Ukrainian counterparts at the scene.

For John Culp, a retired US soldier, there was no doubt the Russians were targeting the park deliberately:

"We are in Gorky Park.. With its paths, its stages etc.. We are investigating the fact that many rockets and shells were fired in and near the park."

"There is no military target here. It was done knowingly to cause terror and fear among the civilian population," he charged.