About 2,000 Ukrainian troops and 1,000 civilians reported to be holed up there

The UN says its humanitarian office is mobilizing an experienced team from around the world to co-ordinate the complex evacuation of civilians from the besieged steel plant in the battered Ukrainian city of Mariupol with the International Committee of the Red Cross (IRCC).

UN Secretary General Antonio Guterres and Russian President Vladimir Putin agreed in principle to UN and ICRC participation in the evacuation from the plant during a nearly two-hour, one-on-one meeting Tuesday.

The sprawling Azovstal complex, which has been almost completely destroyed by Russian attacks, is the last pocket of organized Ukrainian resistance in Mariupol. An estimated 2,000 troops and 1,000 civilians are said to be holed up in bunkers underneath the wrecked structure.

UN deputy spokesperson Farhan Haq told reporters Wednesday that the UN is trying to translate the Guterres-Putin agreement in principle "into an agreement in detail and an agreement on the ground."

"And ultimately what we want is to make sure that a ceasefire would be respected that would allow us to move people safely," he said.

Haq said UN officials are having follow-on discussions Wednesday with authorities in Moscow and Kyiv "to develop the operational framework for the timely evacuation of civilians."

He said the exact timing depends on the outcome of discussions between the UN humanitarian office and Russia's Ministry of Defence in Moscow as well as between the UN crisis co-ordinator for Ukraine, Amin Awad, and the authorities in Kyiv, where Guterres will be meeting Ukraine's President Volodymyr Zelensky on Thursday.

Putin vows victory in Donbas

Putin has vowed to Russia's parliament that the goals of the country's military operation in Ukraine will be achieved.

Putin said in an address on Wednesday to both houses of parliament: "I want to emphasize again that all the tasks of the special military operation we are conducting in the Donbas and Ukraine, launched on Feb. 24, will be unconditionally fulfilled."

That, he said, will "guarantee the security of the residents" of separatist regions in Eastern Ukraine that Russia recognized as independent shortly before launching its military action in Ukraine, as well as Crimea — which Russia annexed in 2014 — "and our entire country in the historical perspective."

Since the Russian invasion force was driven back at the outskirts of Kyiv last month, Moscow has refocused its operation on the Donbas, a mostly Russian-speaking region that ihas been partly held by Kremlin-backed rebels since 2014.

On Wednesday, fighting continued in the Ukraine's east along a largely static front line some 480 kilometres long.

Russia claimed its missiles hit a batch of weapons that the U.S. and European nations had delivered to Ukraine. One person was killed and at least two were injured when rockets hit a residential neighbourhood in Kharkiv.

Western officials, speaking on condition of anonymity to discuss intelligence findings, said Russia has made slow progress in the Donbas, with "minor gains," including the capture of villages and small towns south of Izyum and on the outskirts of Rubizhne.

They said some Russian troops have been shifted from the gutted southern port city of Mariupol to other parts of the Donbas. But some remain in Mariupol to fight Ukrainian forces holed up at the Azovstal steel plant.

The governor of the Luhansk region — which, along with Donetsk, makes up the Donbas — conceded that Russia has made minor progress in its advance on Rubizhne through its nearly constant bombardment, but that Ukrainian troops are fighting back and retreating only when there is nothing left to defend.

"There is no point of staying at the territory that has been fired so often, that every meter is well known," Serhiy Haidai said.

Explosions in Kherson

In the southern Ukrainian city of Kherson, a series of explosions boomed near the television tower late Wednesday and at least temporarily knocked Russian channels off the air, Ukrainian and Russian news organizations reported.

The Russian state news agency RIA Novosti said missiles and rockets were fired at the city from the direction of the Ukrainian forces to the northwest.

Ukrayinska Pravda, an online newspaper, said the strikes set off a fire and knocked Russian television channels off the air.

RIA Novosti said the broadcast later resumed. It said Russian channels began broadcasting from Kherson last week.

Kherson has been occupied by Russian forces since early in the war.

Russia has been determined to strengthen its control over the city, but residents have continued to come out onto the streets to protest the occupation.

Explosions in Russia, Moldova

A Ukrainian presidential adviser has hinted that his country might be involved in a series of fires in border regions of Russia in recent days.

On Wednesday, the governor of the Belgorod region said an ammunition depot was burning after several explosions were heard. Earlier this week, there was a blaze at an oil storage facility in Bryansk.

Ukraine hasn't officially taken responsibility for those and other incidents, and Russian officials haven't publicly ascribed them to Ukrainian attacks.

But Ukrainian presidential adviser Mykhailo Podolyak said in a Telegram post Wednesday that "karma [is] a harsh thing."

He said that Russian regions where the incidents happened "are now also actively studying the concept of `demilitarization."'

Without directly admitting any Ukrainian involvement, he said that "sooner or later the debts will have to be repaid."

To Ukraine's southwest, concern has increased in recent days over the prospect of the conflict widening to neighbouring Moldova, where pro-Russian separatists in the Transnistria region have blamed Ukraine for reported attacks there this week.

Authorities in Transnistria — a sliver of land with about 470,000 people that has been under the control of separatist authorities since a 1992 war with Moldova — said there had been firing across the border from Ukraine on Wednesday.

Ukraine has accused Russia of trying to mastermind 'false flag' attacks in the region, and Moldova's pro-Western government accuses the separatists of trying to stir conflict.

Southern Ukraine and Moldova have been on edge since a senior Russian military officer said last week that the Kremlin's goal is to secure not just Eastern Ukraine but the entire south, so as to open the way to Transnistria.