Ukraine’s recent counter-offensive will not change Russia’s plans, Vladimir Putin has said in his first public comments on the matter.
In a rapid counter-attack, Ukrainian forces say they captured over 8,000 sq km (3,000 sq miles) in six days in the north-eastern Kharkiv region.
But Mr Putin said he was not in a hurry, and the offensive in Ukraine’s Donbas region remains on track.
He also noted that Russia had so far not deployed its full forces.
“Our offensive operation in the Donbas is not stopping. They’re moving forward – not at a very fast pace – but they are gradually taking more and more territory,” he said after a summit in Uzbekistan.
The industrial Donbas region in east Ukraine is the focus of Russia’s invasion, which Mr Putin falsely claims is necessary to save Russian-speakers from genocide.
Parts of the Donbas have been occupied by Russian-backed separatists since 2014. The Kharkiv region, where Ukraine’s recent counter-attack was launched, is not part of the Donbas.
In Friday’s comments, Mr Putin threatened a “more serious” response if Ukrainian attacks continue.
“I remind you that the Russian army isn’t fighting in its entirety… Only the professional army is fighting.”
Russia initially denied sending conscript soldiers to Ukraine, but several officers were disciplined after cases came to light of conscripts being forced to sign contracts and in some instances being taken prisoner.
So far, Russia has not officially declared war on Ukraine and only refers to its invasion as a “special military operation”.
But after Russia’s recent losses, some pro-Kremlin commentators have called for more forces to be mobilised. A recent leaked video which appears to show an attempt to recruit convicts to a private military company suggests Russia is struggling to find enough men willing to fight.
Speaking during an interview with CBS News, Mr Biden said such action would “change the face of war unlike anything since World War Two”.
President Putin put the country’s nuclear forces on “special” alert following its invasion of Ukraine in February.
The Russian leader has rarely left his country since then.
This week’s visit to the Shanghai Co-operation Organisation summit in Uzbekistan – where he met the Chinese leader Xi Jinping – highlights his need to foster ties with Asian countries after being sidelined by the West.
But even there, leaders have expressed concern over the invasion.
“Today’s time is not a time for war,” Indian Prime Minister Narendra Modi told Mr Putin.
And on the previous day, Mr Putin hinted that Xi Jinping also disapproved.
“We understand your questions and concerns” he told the Chinese leader in reference to the war.
