Ukraine live reporting | Putin puts nuclear forces on high alert Russians agree to talks

Reports that Russian President Vladimir Putin has put his nuclear forces on high alert represents an unnecessary and dangerous move, according to the Pentagon.

Putin made the move Sunday in response to “aggressive statements” by leading NATO powers and economic sanctions by the West. The directive means Putin has ordered Russia’s nuclear weapons prepared for increased readiness to launch.

Russia is under no threat from the United States and its NATO allies, and a miscalculation could be dangerous, a senior Defense Department official told reporters on condition of anonymity to discuss intelligence matters.

The Pentagon is confident it can protect the United States and its allies, the official said.

U.S. Ambassador to the United Nations Linda Thomas-Greenfield said Putin is “continuing to escalate” the war in Ukraine in a way that is “unacceptable.”

Meanwhile, the office of Ukrainian President Volodymyr Zelenskyy said a delegation would meet with Russian officials for talks, near the Belarus border.

Thomas-Greenfield expressed hope for prospective peace talks. "We'll look forward to what comes out of those discussions," she told CNN's "State of the Union."

Earlier Sunday, Russian troops entered Kharkiv, Ukraine’s second-largest city, and fighting is underway in the streets, according to the Associated Press. Videos posted on Ukrainian media and social networks showed Russian vehicles moving across Kharkiv and a light vehicle burning on the street. Residents were urged to stay inside.

The troops in Kharkiv arrived after Russia unleashed a wave of attacks on Ukraine, targeting airfields and fuel facilities. Two large explosions rocked an area south of the capital just before 1 a.m. local time. Zelenskyy’s office said one of the blasts was near the Zhuliany airport and the other blast hit an oil depot about 25 miles south of the capital, according to the mayor of Vasylkiv via the AP. Russian forces also blew up a gas pipeline in Kharkiv, according to the Ukrainian president's office.

The U.N. has confirmed at least 240 civilian casualties, including at least 64 people killed in the fighting in Ukraine since Russia’s invasion on Thursday, according to AP. Though, the U.N. believes the toll may be "considerably higher.”