Suspected Russian missile strikes hit downtown Kyiv on Thursday as U.N. Secretary-General Antonio Guterres was in the Ukrainian capital for efforts to rekindle peace talks.

Agence France-Presse (AFP) correspondents saw a building in flames and black smoke pouring into the air with a heavy presence of police and rescuers in the area, a residential neighborhood on the western side of the city.

Kyiv Mayor Vitali Klitschko said there had been "two hits in the Shevchenkovsky district," with one hitting "the lower floors of a residential building." He said three people had been taken to the hospital but the extent of their injuries was not immediately clear.

A close aide to the U.N. chief sent a message to journalists confirming they were safe.

The explosions occurred after U.N. chief Guterres completed talks with Ukrainian President Volodymyr Zelenskyy focusing on efforts to evacuate civilians from the Russian-besieged southern port of Mariupol.

Guterres told Portuguese broadcaster RTP when asked about the blasts: "There was an attack on Kyiv ... it shocked me, not because I'm here but because Kyiv is a sacred city for Ukrainians and Russians alike."

Zelenskyy's chief of staff, Andriy Yermak, said the blasts were "proof that we need a quick victory over Russia ... We must act quickly – more weapons, more humanitarian efforts ... because every day Ukraine pays a high price for the protection of democracy and freedom."

The move prompted a furious response from Ukraine's government, with Foreign Minister Dmytro Kuleba denouncing it as a "heinous act of barbarism," which demonstrated Russia's "attitude towards Ukraine, Europe and the world."

Defense Minister Oleksiy Reznikov also lashed out, writing on Twitter: "This is an attack on the security of the Secretary-General and on world security!"

The strikes came just two days after Guterres held talks in Moscow with Vladimir Putin, with the Russian leader telling him he remained hopeful that negotiations could end the conflict.

The irony of the timing was not lost on Mykhaylo Podolyak, a senior Zelenskyy aide.

"Missile strikes in the downtown of Kyiv during the official visit of @antonioguterres. The day before, he was sitting at a long table in the Kremlin, and today explosions are above his head," he tweeted.

Earlier, on his first visit to Ukraine since Russia launched a full-scale invasion on Feb. 24, Guterres toured several towns and villages near Kyiv where Russian forces are accused of killing civilians.

"War is an absurdity in the 21st century. The war is evil," he said after visiting places, including Bucha, where dozens of bodies in civilian clothes were found, some with their hands bound and others buried in shallow graves.

Later at a joint press conference in Kyiv with Zelenskyy, Guterres admitted the Security Council had failed to go far enough in its efforts to "prevent and end" Russia's war in Ukraine.

"Let me be very clear: the Security Council failed to do everything in its power to prevent and end this war. And this is the source of great disappointment, frustration and anger," he said.