Russia-Ukraine conflict: EU Council chief Charles Michel arrives in Kyiv

Kyiv: European Council chief Charles Michel, representing EU member states, arrived in Kyiv on Wednesday as Russia continues its new offensive in the east of Ukraine.

"In Kyiv today. In the heart of a free and democratic Europe," Michel wrote on his Twitter account, accompanied by a photo taken at a train station in the Ukrainian capital.

Ukraine received fighter jets to help resist the Russian invasion, as Moscow intensified its offensive in the east where a besieged officer in Mariupol warned Wednesday his forces were facing their "last days, if not hours".

The West has responded to a renewed Russian push into the Donbas region with fresh weapons for Kyiv and a push to increase "Moscow's international isolation".

The Pentagon said that Ukraine had recently received fighter planes and parts to bolster its air force, declining to specify the number of aircraft and their origin.

Kyiv has asked its Western partners to provide MiG-29s, which its pilots already know how to fly and a handful of Eastern European countries have.

Control of Donbas and the southern port of Mariupol would allow Moscow to create a southern corridor to the Crimean peninsula that it annexed in 2014, depriving Ukraine of much of its coastline.

In the latest ultimatum issued in its battle to capture Mariupol, Moscow made another call for the city's defenders to surrender on Wednesday by 2 pm Moscow time (1100 GMT) and announced the opening of a humanitarian corridor for any Ukrainian troops who agreed to lay down their arms.

As the deadline approached, a commander in the besieged Azovstal power 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," Serhiy Volyna from the 36th Separate Marine Brigade said.

"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."

Thousands of troops and civilians remain holed up in the plant.

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

During an interview broadcast on CNN Tuesday, Pavlo Kyrylenko - who oversees the Donetsk region's military administration - insisted Mariupol remained contested.

"The Ukrainian flag is flying over the city," he said. "There are certain districts where street fighting is continuing. I can't say the Russians are controlling them."

Offering some respite, Kyiv said early Wednesday it had agreed with Russian forces to open a safe route for civilians to flee the devastated city.

"We have managed to get a preliminary agreement on a humanitarian corridor for women, children and elderly persons," Deputy Prime Minister Iryna Vereshchuk wrote on Telegram.