US President Joe Biden’s personal insults against Russian President Vladimir Putin narrow the window of opportunity for improving relations between Moscow and Washington, Kremlin Spokesman Dmitry Peskov told TASS on Saturday.

"A state leader should control his temper, nonetheless," Peskov said commenting on the latest remark from the US president.

"And, of course, each time such personal insults [are uttered, they] narrow the window of opportunity for our bilateral relations under the current [US] administration. It is necessary to be aware of this," Peskov stressed.

The Kremlin spokesman was surprised that Biden, who was an enthusiastic proponent of bombing Yugoslavia in 1999, voiced such assertions against Putin.

"After all, he is the man who once demanded, when speaking on TV in his country that Yugoslavia be bombed. That’s right, that Yugoslavia be bombed. He demanded to kill people," Peskov told TASS.

"Therefore, it is certainly bizarre to hear such a thing from him," he insisted.

On Saturday, Biden visited a center for Ukrainian refugees at a stadium in Warsaw. The White House said that Biden had talked to the refugees and volunteers. When asked by a reporter what he thought of Putin and of what is happening in Ukraine, Biden retorted: "He’s a butcher."

On March 21, US Ambassador to Russia John Sullivan was summoned to the Russian Foreign Ministry, which issued a demarche and handed him a note of protest in connection with Biden’s recent unacceptable remarks regarding the Russian president. On March 17, Biden uttered more inimical comments about his Russian counterpart, branding him a "murderous dictator, a pure thug who is waging an immoral war against the people of Ukraine." A day earlier, when asked by a reporter, the US president said he considered Putin a "war criminal." Peskov told TASS then that these remarks were unacceptable and unforgivable.

TASS