Ukraine and Russia late Thursday reached an understanding on joint provision of humanitarian corridors to evacuate civilians as the second round of negotiations between the parties continues. The agreement also includes a temporary cease-fire during evacuations.

Ukrainian presidential adviser Mykhailo Podolyak said that the sides had discussed humanitarian corridors and agreed to speak again.

"To our great regret, we did not get the results we were counting on," Podolyak said.

Previously, Ukrainian President Volodymyr Zelenskyy asked his Russian counterpart Vladimir Putin to "stop this war," underlining the need for the two leaders to speak without preconditions.

Moscow and Kyiv began a second round of talks in western Belarus earlier on the same day, just hours after Putin reiterated his country's demands in a telephone conversation with his French counterpart Emmanuel Macron.

The talks are taking place in western Belarus, with the Russian delegation led by presidential adviser Vladimir Medinsky and his Ukrainian counterpart led by David Arachamija, the head of President Volodymyr Zelenskyy's ruling party.

Both sides had agreed on the Brest region in western Belarus as the venue for the talks and the Russian military planned a "security corridor" to allow the Ukrainian delegation's passage.

Ukraine's Foreign Ministry has urged Russia to declare a cease-fire in the hard-hit eastern regions of Kharkiv and Sumy to allow civilians to reach safety. Meanwhile, the United Nations also warned more than 10 million people might leave their homes due to Russia's invasion of Ukraine.

The first negotiations on Monday at the Belarusian-Ukrainian border brought no tangible results. Russian attacks continued to pummel Ukraine, and several explosions were registered in Kyiv early Thursday, the eighth day of the invasion, triggering air raid sirens.

In a phone call with Macron, Putin reiterated Russia's call for the demilitarization of Ukraine, as well as its inability to join the NATO military alliance.

At the same time, the Kremlin threatened, "Attempts to gain time by dragging out the negotiations will only lead to additional demands on Kyiv in our negotiating position."

Meanwhile, pro-Russian separatists "tightened their circle" around the strategically important city of Mariupol in southern Ukraine, a Defense Ministry spokesperson in Moscow said Thursday.

Igor Konashenkov claimed that the forces had gained control of three more communities in the area surrounding Mariupol, according to Russian news agencies. They also reportedly took over the city of Balakleya, southeast of the city of Kharkiv.

These claims could not be independently verified.

Mariupol residents had been offered the opportunity to head east toward separatist-controlled areas the previous day.

Konashenkov again said that Russia was "taking measures to ensure the security of civilians," despite mounting reports of missile strikes on urban residential areas across Ukraine.

The defense official said civilians could leave the embattled village of Borodyanka "through a specially designated corridor." The offer is seen as a harbinger of a major Russian attack.

There is an airfield near Borodyanka.

According to the Russians, 62 Ukrainian aircraft, 53 drones and more than 600 tanks and armored vehicles have been destroyed since the invasion began last week, as well as a total of 1,612 military objects.

Konashenkov did not give any information on casualties suffered by the Russian side. On Wednesday, Moscow had said that 498 Russian soldiers have been killed. Kyiv claims Russian losses are much higher.

The news comes several days after Putin ordered the country's deterrent weapons be put on special alert.

However, Russian Foreign Minister Sergei Lavrov dismissed Western countries' alarm over a possible nuclear escalation as "scaremongering."

"Everyone knows that a third World War can only be a nuclear one," Lavrov said. "I assure you that we will not allow provocations that make us lose our balance," he warned.

Also on Thursday, Germany's Economy Ministry approved the delivery of 2,700 anti-aircraft missiles to Ukraine, a dramatic political shift after a long-standing export ban on weaponry to Ukraine.