Ukrainian President Volodymyr Zelenskyy has called for Russian President Vladimir Putin to meet him, salting the proposal with sarcasm. 

"Sit down with me to negotiate, just not at 30 metres," he said on Friday (NZT), apparently referring to recent photos of Putin sitting at one end of an extremely long table when he met with French President Emmanuel Macron. 

"I don't bite. What are you afraid of?" Zelenskyy said. 

During Thursday's news conference, Zelenskyy said that prospects for the ongoing diplomatic talks didn't seem promising, but emphasised the need to negotiate, adding that "any words are more important than shots".

He also said the world was too slow to offer support for Ukraine and prodded Western leaders to enforce a no-fly zone over Ukraine to deny access to the Russian warplanes. The US and Nato allies have ruled out the move that would directly pit Russian and Western militaries.

Zelenskyy charged that if the West remains reluctant to declare a no-fly zone over Ukraine, it should at least provide Kyiv with warplanes.

The second round of talks between the two sides concluded on Friday (NZT).

A Ukrainian official who attended said that "regrettably, we haven't reached results we were hoping for," but emphasised the importance of humanitarian corridors, saying that many cities have been besieged by the Russian troops and are experiencing a dramatic shortage of food and medicines.

The establishment of safe corridors was the Ukrainians' main demand heading into their second round of negotiations in Belarus, in the Brest region that borders Poland.

Ukraine's presidential adviser Mykhialo Podolyak said that Russia and Ukraine will quickly set the necessary channels of communications and logistics to organise those safe corridors.

Podolyak added that a third round of talks between the two sides will be held shortly.

Putin said the Russian military would offer safe corridors to civilians to allow them to leave areas of fighting.

Putin, speaking in a video call with members of his Security Council, charged that Ukrainian nationalist groups were preventing people from leaving.

Russian President Vladimir Putin chairs a Security Council meeting. Photo / AP

French President Emmanuel Macron said Friday (NZT) that he again asked Putin to halt attacks on Ukraine, but that the Russian leader wouldn't agree to it.

"At this point, he refuses," Macron wrote in a Twitter post.

Macron confirmed that he had spoken to Putin on the phone earlier and said he will continue the dialogue to prevent "more human tragedy".

"We must prevent the worst from happening," Macron said in his post. Dialogue has to continue to "protect the [civilian] population, to obtain goodwill gestures ... to put an end to this war".

French President Emmanuel Macron makes a television nationwide address on the situation in Ukraine. Photo / AP

Today's developments came after Russian forces laid siege to two strategic Ukrainian seaports and pressed their bombardment of the country's second-biggest city, while the huge armoured column threatening Kyiv appeared stalled outside the capital.

The strategically crucial Ukrainian city Kherson has become the first to be captured by Russia, with officials confirming Putin's forces now had "complete control". 

Kherson has about 300,000 residents, and its capture could enable Russia to control a significant chunk of the southern coastline and allow troops to head west towards the port city of Odessa. 

Mayor Igor Kolykhaev confirmed Russian troops had encircled the city with Ukrainian forces retreating to the nearby city of Mykolaiv. 

Russia has claimed victory over the city, with Defence Ministry spokesman Igor Konashenkov stating that Kherson was under the "complete control" of Russian forces. 

He claimed in a statement that Russian authorities were in talks with Ukrainian leaders and that Kherson's infrastructure was still operational. 

Ukrainian President Volodymyr Zelenskyy on a working trip to Kherson early last month. Photo / AP 

The mayor of Enerhodar, site of Europe's largest nuclear plant, says Ukrainian forces are battling Russian troops on the edges of the city. 

Enerhodar is a major energy hub on the left bank of the Dnieper River and the Khakhovka Reservoir that accounts for about one quarter of the country's power generation due to the Zaporizhzhia nuclear plant, which is Europe's largest. 

Dmytro Orlov, the mayor of Enerhodar, said Thursday that a big Russian convoy was approaching the city and urged residents not to leave homes. 

Ukraine's state emergencies agency also says that at least 22 civilians have been killed in a Russian strike on a residential area in the city of Chernihiv, a city of 280,000 in Ukraine's north. Rescuers are continuing to look through debris for more bodies. 

The UN human rights chief says military operations in Ukraine are "escalating further as we speak" and warned of "concerning reports" of the use of cluster bombs. 

Michelle Bachelet said the Ukrainian town of Volnovakha in the eastern Donetsk region, where pro-Russian separatists seized territory in 2014, leading to a drawn-out military conflict, "has been almost completely destroyed by shelling," with residents hiding in basements. 

She spoke Thursday during an "urgent debate" at the Human Rights Council, where country after country spoke out against Russia's invasion. Many Western envoys sported blue or yellow ties, scarves, jackets or ribbons on their lapels – colours of the Ukrainian flag. 

Delegates will vote Friday on a resolution that would create a three-person panel of experts to monitor human rights and report on rights abuses and violations in Ukraine. 

Pro-Russian separatists stand next to a burned vehicle near a damaged by shelling building in Donetsk. Photo / AP 

In an earlier videotaped address,Zelenskyy called on Ukrainians to keep up the resistance. He vowed that the invaders would have "not one quiet moment" and described Russian soldiers as "confused children who have been used". 

Moscow's isolation deepened when most of the world lined up against it at the United Nations to demand it withdraw from Ukraine. And the prosecutor for the International Criminal Court opened an investigation into possible war crimes. 

Ukrainian officials fear large numbers of people may be dead after "more than 15 hours" of shelling on Mariupol near the Russian border. 

Mayor Vadym Boychenkos said Russian troops had prevented citizens from fleeing to safety. 

"There's been colossal destruction of residential infrastructure, there are many wounded and unfortunately many civilian dead, women, children, old people," he said. 

"A full-scale genocide of the Ukrainian people is underway. 

"You have to understand that the occupation forces of the Russian Federation have done everything to stop the exit of civilians from our city of half a million people." 

Mariupol is seen as especially strategic for the invading forces, as it would allow pro-Russian separatists to link up with troops positioned in Crimea. 

However, a massive, 64km-long convoy of Russian troops and vehicles heading to Kyiv has been hit by major logistic nightmares, with "no appreciable movement closer to the city" made over the past two days. 

That's according to a senior Pentagon official, who claimed Russian forces were now facing serious food and fuel shortages. 

The official added that Ukrainians had been strongly resisting north of the capital, and had potentially also "at places and times" targeted the convoy, according to the New York Times. 

Russia reported its military casualties for the first time since the invasion began last week, saying nearly 500 of its troops have been killed and almost 1600 wounded. 

Ukraine did not disclose its own military losses but said more than 2000 civilians have died, a claim that could not be independently verified.