The Kremlin has called comments by US president Joe Biden about his Russian counterpart Vladimir Putin "personal insults" and said Mr Biden's remarks appeared to have been fuelled by irritation, fatigue and forgetfulness.
Mr Biden labelled Mr Putin a "war criminal" and a "murderous dictator" in recent days after the Russian leader last month sent tens of thousands of troops into Ukraine in what he called a special operation to degrade its military capabilities and root out people he called dangerous nationalists.
"We hear and see statements that are actually personal insults to President Putin," Kremlin spokesperson Dmitry Peskov told reporters.
"Given such irritability from Mr Biden, his fatigue and sometimes forgetfulness...fatigue that leads to aggressive statements, we will not make harsh assessments, so as not to cause more aggression."
Ukrainian forces have mounted stiff resistance against Russian forces and the West has imposed sweeping sanctions on Moscow in an effort to force it to withdraw.