According to The Kyiv Independent, Ukrainian President Volodymyr Zelensky agreed on Sunday to send a Ukrainian delegation to Russia to negotiate near Ukraine's border with Belarus.

As per Axios, Zelensky said that the discussions would take place "without prerequisites."

During a contact with Zelensky, Belarusian President Alexander Lukashenko, who permitted Russian President Vladimir Putin to utilize Belarus as a staging ground for his invasion, organized the meeting.

Despite their agreement, the two presidents do not get along.

Per the Associated Press, Zelensky addressed the Belarusian people directly on Sunday, asking how they could "look into the eyes of their children" as Russian troops "killed our children" with missiles launched from Belarus.

Lukashenko retaliated by labeling Zelensky a puppet of the United States. Since the invasion began, Lukashenko has also reinforced his connections with Putin.

Lukashenko informed French President Emmanuel Macron on Saturday that if NATO installed nuclear weapons in Poland or Lithuania, he would allow Russia to deploy nuclear weapons in Belarus, per the Russian news agency Interfax.

Belarusian voters went to the polls on Sunday to vote in a constitutional referendum that would allow Lukashenko, who has been president since 1994 and is 67 years old, to stay in office until 2035 and allow for greater collaboration with Russia, according to the Associated Press.

Russian troops advancing south from Belarus toward Kyiv, Ukraine's capital, have dispatched reconnaissance soldiers to the city, which engaged in combat with the Ukrainian military on Friday night.

The city is yet to be attacked by the main division of Russian soldiers.

The news of the meetings came as Russian President Vladimir Putin stated on Sunday that in response to recent sanctions and "aggressive words" from NATO members, he had placed Russia's nuclear-deterrent troops on high alert.

Putin said in a televised statement that he had ordered a "special regime of combat duty" for the nuclear deterrent troops.

The announcement comes on the fourth day of conflict in Ukraine since Russia entered the country. 

Before daybreak on Sunday, Russian forces stormed Kharkiv, Ukraine's second-largest city, engaged in urban fighting and blowing up a gas pipeline in the city.

Russian forces assaulted airfields and fuel facilities in other areas, but Ukrainian forces held on to Kyiv, the capital.

According to the Associated Press, two explosions were heard shortly before 1 a.m., local time, with Ukrainian President Volodymyr Zelensky claiming one occurred near the Zhuliany airport and the mayor of Vaslykiv claiming the second occurred at an oil storage 25 miles south of the city.