Ukraine said Friday that its forces had recaptured chunks of territory around the embattled city of Bakhmut, even as President Volodymr Zelensky insists his army needs more time before launching an expected spring offensive.

Kyiv's claimed gains near the epicentre of the war's fiercest battle have been refuted by Moscow, but come as expectations build over the anticipated, high-stakes fightback.

China said it would send a special envoy next week to visit Ukraine, Russia and European nations as Beijing pursues efforts to cast itself as peacemaker. 

Beijing plans to send its high-ranking diplomat Li Hui to Ukraine, Poland, France, Germany and Russia to "communicate with all parties on the political settlement of the Ukraine crisis".

From Ukraine to the Middle East, Beijing in recent months has sought to position itself as a mediator with a leading role in solving the world's crises.

But while China says it is a neutral party on the Ukraine war, it has been criticised for refusing to condemn Moscow for the invasion.

- 'Great losses' in Bakhmut fight -

On the battlefield, Ukraine said its forces advanced two kilometres (around one mile) near Bakhmut -- the scene of the longest and bloodiest battle since Moscow's more than year-long invasion. 

Bakhmut once had a population of around 70,000 people. It has been destroyed as Russian forces have posted incremental gains over recent months, amounting to some 80 percent of the city. 

"The enemy has suffered great losses of manpower," Deputy Defence Minister Ganna Malyar said in a statement on social media. 

"We did not lose a single position in Bakhmut this week."

Russia has denied Ukraine made any breakthroughs in the flashpoint city, saying that reports of its territorial losses around the city did "not correspond to reality".

But the head of the Wagner private military group spearheading Moscow's attack on Bakhmut, Yevgeny Prigozhin, said Kyiv had made "successful counterattacks". 

The social media accounts of several Russian war correspondents late at night also spread alarm, with some of them saying Kyiv's long-anticipated counteroffensive had begun.  

Zelensky, however, has said in an interview published Thursday that Kyiv needs more time before going on the offensive. 

"Mentally we're ready...," the Ukrainian leader noted. "In terms of equipment, not everything has arrived yet.

"With (what we have) we can go forward and be successful. But we'd lose a lot of people. I think that's unacceptable. So we need to wait. We still need a bit more time," he said.

Prigozhin, whose feud with Russia's conventional army has flared in recent days, acknowledged Ukrainian successes and challenged his rival, Defence Minister Sergei Shoigu, to visit Bakhmut. 

"The enemy has launched a number of successful counterattacks," Prigozhin wrote to Shoigu on social media, urging him "to independently assess the current situation". 

- Talks on renewing grain deal -

The message came after the outspoken Wagner chief made unprecedented attacks against Russia's military leadership, accusing Shoigu of being partly responsible for massive Russian losses and saying Russian soldiers were fleeing "criminal" orders in Bakhmut.  

Prigozhin has for days acknowledged that some Ukrainian units were successfully breaking through in some areas. 

The Russian army, however, denied claims by Prigozhin and pro-Moscow bloggers that Kyiv had made some breakthroughs. 

"The individual declarations on Telegram about a 'breakthrough' on several points on the front line do not correspond to reality," the defence ministry said in a statement.

As the fate of Bakhmut hangs in the balance, Turkey said Friday that talks to extend a deal allowing grain exports from Ukraine via the Black Sea following the Russian invasion were nearing an agreement.

"We are heading toward an agreement on the extension of the grain deal," Turkish Defence Minister Hulusi Akar said in a statement. 

The Black Sea Grain Initiative, in place since July after diplomacy by the United Nations and Turkey, allows Ukraine grain exports via port, helping ease shortages and resulting price spikes triggered by Russia's invasion of the breadbasket nation.

bur/kjm