Heraldo de Madrid - Troops defending battered Mariupol plead for outside help

Raising tensions, Russia meanwhile said it had tested a new nuclear-capable intercontinental ballistic missile. The United States said it had been notified and the test was not deemed a threat.

In the latest ultimatum issued in its battle to capture Mariupol after a two-month siege, Moscow made another call for the city's defenders to surrender by 1100 GMT.

It announced the opening of a humanitarian corridor for any Ukrainian troops who agreed to lay down their arms.

Kyiv said early Wednesday it had agreed with Russian forces to open a safe route for civilians to flee the devastated city. But Deputy Prime Minister Iryna Vereshchuk said later the bid "did not work" and efforts would resume Thursday.

A commander in the besieged Azovstal steel plant 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 early Wednesday.

"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."

- EU vows to help Ukraine win -

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 Ukrainian President Volodymyr Zelensky.

But Zelensky said Ukraine still did not have enough weapons to resist the invasion, despite military aid from Western allies.

"The situation in Mariupol is deteriorating" with thousands of troops and civilians stuck in the city, Zelensky said.

"There are two ways to unblock Mariupol. The first one is serious armed assistance. So far, we do not have enough such hardware. The second one is diplomatic, but so far Russia does not agree."

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

- Eastern offensive -

Control of Mariupol and the separatist-controlled eastern Donbas region would allow Moscow to create a southern corridor to the Crimean Peninsula that it annexed in 2014, depriving Ukraine of much of its coastline.

Fighting flared back up this week after Russia launched a major offensive into Donbas.

The battle for Mariupol appeared to be nearing a tipping point, after nearly two months of devastating fighting that has seen untold numbers of civilians trapped and killed.

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

Svyatoslav Palamar, a commander in the nationalist Azov battalion defending Mariupol, said the Russian attack on the sprawling complex was relentless.

"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 Palamar in a post on Telegram.

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

- 'Violent deaths' -

Elsewhere on the frontlines, Ukraine's defence ministry reported its troops had beaten back a Russian attack in the city of Izium, south of the partly blockaded second city of Kharkiv in the east.

Kyiv also claimed enemy losses in a Ukrainian counter-attack near the town of Marinka in Donetsk.

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

In eastern Ukraine's Kramatorsk, a large city in the Donetsk region, residents were already 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 the capital Kyiv.

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

In the car park of the small communal morgue, the 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" and were shot, Lobas said.

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

- 'War crimes' -

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

Russian Foreign Minister Sergei Lavrov accused "nationalist" Ukrainian forces of using civilians as human shields and of refusing to evacuate via humanitarian corridors.

But his forces have faced allegations of war crimes -- most recently from the EU's Michel, who toured the devastated nearby town of Borodianka Wednesday.

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

Putin said the test of the Sarmat intercontinental ballistic missile Wednesday would make the Kremlin's enemies "think twice".

US Department of Defense Spokesman John Kirby said Moscow "properly notified" Washington of the test under an arms treaty.

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R.Parra--HdM