Ukraine claimed Friday to have retaken swathes of ground near the frontline city of Bakhmut, as Russia reported having repelled an attack along a broad stretch of the front line.
The rival reports from the battlefront indicated an increase in fighting after months of relative stability, as expectations grow over Kyiv's spring offensive.
Yevgeny Prigozhin, the head of the Wagner mercenary group, who is spearheading Moscow's attack on Bakhmut, accused the Russian army of "fleeing" from around the eastern Ukraine city.
The question of when and where Ukraine might launch its high-stakes fightback has been the subject of steady speculation, even after President Volodymyr Zelensky insisted this week that his army needed more time to prepare.
The fresh fighting came as China said it would send a special envoy next week to Europe as Beijing pursues efforts to cast itself as a 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 criticized for refusing to condemn Moscow for the invasion.
Zelensky is also expected in Rome on Saturday for talks with political leaders and possibly Pope Francis, his first visit to Italy since Russia's invasion.
'Great losses' in Bakhmut fight
On the battlefield, Ukraine said its forces had advanced two kilometers (around one mile) near Bakhmut — the scene of the longest and bloodiest battle since Moscow's more than year-long invasion.
Bakhmut, which once had a population of around 70,000 people, has been destroyed as Russian forces posted incremental gains in recent months, amounting to some 80% of the city.
Moscow denied Ukraine had made any breakthroughs in the flashpoint city, adding on Friday that it had repelled Kyiv's forces along more than 95 kilometers (60 miles) of the front near the eastern town of Soledar.
Russia's Defense Ministry said Ukraine had deployed more than 1,000 military personnel and up to 40 tanks.
Wagner chief Prigozhin however said Moscow's conventional army "simply went fleeing from the flanks" near Bakhmut.
Prigozhin insisted that "the flanks are failing, the front is collapsing" in that area and said Russia's leadership was downplaying the gravity of the situation.
"For this reason, we must stop lying immediately," Prigozhin said in a video statement released on social media.
The social media accounts of several Russian war correspondents also spread alarm late Thursday, with some saying Kyiv's long-anticipated counteroffensive had begun.
Zelensky, however, said in an interview published Thursday that Kyiv needed 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," he added.
"I think that's unacceptable. So we need to wait. We still need a bit more time."
Prigozhin, whose long-running feud with Russia's conventional army has flared in recent days, acknowledged Ukrainian successes.
He even challenged his rival, Defense 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."
Grain deal talks
Prigozhin has for days reported that some Ukrainian units were successfully breaking through in some areas, as have some pro-Moscow bloggers.
The Russian army, however, has denied such claims.
"The individual declarations on Telegram about a 'breakthrough' on several points on the front line do not correspond to reality," the Defense Ministry said in a statement Thursday.
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 Defense 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.