Ukraine called Wednesday for urgent negotiations with Russia in Mariupol, which appeared close to falling after weeks of siege, as Vladimir Putin flexed his military muscle with the test launch of a new, nuclear capable ICBM.

Washington downplayed the test of the intercontinental ballistic missile and said it had been notified in advance, but Putin said it would make the Kremlin's enemies "think twice", raising tensions nearly two months after he invaded Ukraine and ignited a global crisis.

Map of Ukraine showing civilian casualties recorded by the NGO Acled from the beginning of the conflict on February 24.
Map of Ukraine showing civilian casualties recorded by the NGO Acled from the beginning of the conflict on February 24. AFP / Sylvie HUSSON

Mariupol, a strategic port city on the Sea of Azov, has been under a horrific siege almost since the invasion began. On Wednesday, Moscow issued another call for the devastated city's defenders to surrender.

But Kyiv proposed a "special round" of talks with Moscow, without any conditions, in Mariupol itself.

"One on one. Two on two. To save our guys, Azov, military, civilians, children, the living & the wounded. Everyone. Because they are ours," wrote top Ukraine negotiator and presidential aide Mykhailo Podolyak on Twitter.

A man looks at his destroyed apartment in a residential building outskirts of Kharkiv
A man looks at his destroyed apartment in a residential building outskirts of Kharkiv AFP / SERGEY BOBOK

He tweeted after a Ukrainian commander in the besieged Azovstal steel plant in Mariupol issued a desperate plea for help, saying his marines were "maybe facing our last days, if not hours".

"The enemy is outnumbering us 10 to one," said Serhiy Volyna from the 36th Separate Marine Brigade.

"We appeal and plead to all world leaders to help us. We ask them to use the procedure of extraction and take us to the territory of a third-party state."

A destroyed residential area in the village of Moshchun, northwest of Kyiv, on April 20, 2022
A destroyed residential area in the village of Moshchun, northwest of Kyiv, on April 20, 2022 AFP / Genya SAVILOV

An adviser to the city's mayor described a "horrible situation" in the encircled steel plant and reported that up to 2,000 people -- mostly women and children -- are without supplies of drinking water, food and fresh air.

"Powerful bombs have been dropped several times on Azovstal, we have been bombed from boats... we are under siege. The front is 360 degrees," said Svyatoslav Palamar, a commander in the nationalist Azov battalion defending the city, in a post on Telegram.

Mother of Volodymyr Karas, a Ukrainian serviceman who died during the fighting with Russian troops, reacts during the funeral ceremony at Independence square in Kyiv, on April 20, 2022
Mother of Volodymyr Karas, a Ukrainian serviceman who died during the fighting with Russian troops, reacts during the funeral ceremony at Independence square in Kyiv, on April 20, 2022 AFP / Sergei SUPINSKY

"The situation is critical, we call on international leaders to help the children," he added.

Mariupol has become a symbol of Ukraine's unexpectedly fierce resistance since Russian troops invaded the former Soviet state on February 24.

Capturing it would allow Russia to have a land bridge between the Crimea peninsula, which it annexed in 2014, and the two Moscow-backed separatist statelets in Ukraine's east.

Ukraine's President Volodymyr Zelensky reacts during a press conference following his talks with President of the European Council in Kyiv
Ukraine's President Volodymyr Zelensky reacts during a press conference following his talks with President of the European Council in Kyiv AFP / Sergei SUPINSKY

The offer of talks came after Kyiv said it had agreed with Russian forces to open a safe route for civilians to flee the devastated city -- but that the had attempt failed.

Workers take a break next to body bags as they exam the bodies of victims at a morgue in Bucha, on April 19, 2022, during the Russian invasion of Ukraine
Workers take a break next to body bags as they exam the bodies of victims at a morgue in Bucha, on April 19, 2022, during the Russian invasion of Ukraine AFP / Yasuyoshi CHIBA

As fighting raged in Ukraine's east and south, European Council leader Charles Michel visited Kyiv and vowed the EU would do "everything possible" to help Ukraine win the war.

"You are not alone. We are with you," Michel said during a press conference alongside Ukraine's President Volodymyr Zelensky.

Zelensky said his country still did not have enough weapons to resist the invasion, despite billions in military aid from Western allies -- though, in a video message he added his partners "understand our needs better."

Nadiya (L), and Natalia (R), both 62, walk amid debris of their destroyed houses in the village of Moshchun, northwest of Kyiv
Nadiya (L), and Natalia (R), both 62, walk amid debris of their destroyed houses in the village of Moshchun, northwest of Kyiv AFP / Genya SAVILOV

Ahead of Michel's arrival, the Pentagon said Ukraine had received fighter planes to bolster its air force -- but later it corrected that statement, saying only aircraft parts had been delivered.

Washington has repeatedly vowed to do everything it can to help Kyiv, without igniting a direct conflict with nuclear-armed Russia.

On Wednesday US President Joe Biden said he has been "amazed" by Ukrainian resistance.

"They're tougher and more proud than I thought," he said, adding that Western "weapons and ammunition are flowing in daily."

He said NATO remains "united, focused and energized," adding: "I don't think Putin counted on it."

Russia said Wednesday its forces had launched 73 air strikes across Ukraine, hitting dozens of locations where Ukrainian troops were concentrated.

In eastern Ukraine's Kramatorsk, a large city in the Donetsk region, residents were bracing for the worst.

"It's going to be a mess," said Alexander, 53. "There's nothing good to expect."

Further from the frontlines, residents were still reeling weeks after Russian forces withdrew from the area near Kyiv.

At a morgue in Bucha, families carefully searched body bags and examined cadavers looking for missing loved ones.

In the car park body bags arrived in carts or were piled up in trailers, vans and non-refrigerated trucks.

Four hundred bodies have been discovered there since the Russians withdrew on March 31, local police chief Vitaly Lobas told AFP. Around a quarter of them are still unidentified.

"The majority died violent deaths," Lobas said.

Ukrainian authorities have said that over 1,200 bodies have been found in the Kyiv region so far.

Putin has said he launched the so-called military operation in Ukraine to save Russian speakers there from a "genocide" carried out by a "neo-Nazi" regime.

"History will not forget the war crimes that have been committed here," Michel wrote on Twitter.