A Russian delegation will be sent to an undisclosed location to await a possible second round of talks with Ukraine on Wednesday, Kremlin spokesman Dmitry Peskov said.

"Our delegation will be waiting for the Ukrainian negotiators on-site this afternoon, closer to the evening," Peskov told reporters Wednesday, noting that he would not be revealing the location for now.

"We can try to predict whether Ukrainian negotiators will show up or not. Let's hope this happens," he added. "Our [negotiators] will be there and ready."

The head of the Russian delegation, Vladimir Medinsky, has said that they would be on the Belarus-Poland border but there's been no confirmation of that location.

Ukraine has not yet confirmed that it will take part in the talks with Russia on Wednesday. Ukrainian Foreign Minister Dmytro Kuleba said earlier that his country was ready to negotiate but that Russia had not changed its position and was still issuing ultimatums.

Wednesday's talks would follow a meeting between both sides near the Belarus-Ukraine border on Monday that failed to reach a breakthrough.

-ABC News' Patrick Reevell

Russian Foreign Minister Sergey Lavrov warned Wednesday that if a third world war were to take place, it would involve nuclear weapons and be destructive, according to Russian state-owned news agency RIA Novosti.

Jailed Russian opposition leader Alexei Navalny is urging people in Russia and around the world to stage daily protests against Russia's invasion of Ukraine.

"We -- Russia -- want to be a nation of peace. Alas, few people would call us that now," Navalny said Wednesday in a series of posts on Twitter via his spokesperson. "But let's at least not become a nation of frightened silent people. Of cowards who pretend not to notice the aggressive war against Ukraine unleashed by our obviously insane czar."

"They say that someone who cannot attend a rally and does not risk being arrested for it cannot call for it. I'm already in prison, so I think I can," he tweeted. "We cannot wait any longer. Wherever you are, in Russia, Belarus or on the other side of the planet, go to the main square of your city every weekday and at 2 pm on weekends and holidays."

"Yes, maybe only a few people will take to the streets on the first day. And in the second -- even less," he added. "But we must, gritting our teeth and overcoming fear, come out and demand an end to the war. Each arrested person must be replaced by two newcomers."

Navalny called on people to not just "be against the war" but to "fight against the war."

"If in order to stop the war we have to fill prisons and paddy wagons with ourselves, we will fill prisons and paddy wagons with ourselves," he tweeted. "Everything has a price, and now, in the spring of 2022, we must pay this price. There's no one to do it for us."

Navalny, the most prominent critic of Russian President Vladimir Putin and the Kremlin, was imprisoned last year when he returned to Russia from Germany after recovering from an attempted assassination with nerve agent poisoning in Siberia. Russia has denied carrying out such an attack.

Ukrainian President Volodymyr Zelenskyy warned Wednesday that the international community "can't stay neutral," as the Russian invasion entered its seventh day.

"Neutral Switzerland has supported EU sanctions against Russian oligarchs, officials, the state, and companies. Once again - neutral Switzerland. So why do other countries wait?" Zelenskyy said in a televised address. "Our anti-war coalition has already been joined by those countries that Moscow was counting on a week ago. This is an extraordinary result. You can't stay neutral right now."

"We are in our homeland and there will be an international tribunal for waging the war against us," he added.

Zelenskyy also praised his fellow Ukrainians for being "united."

"During this time, we have truly become one," he said. "Today you, Ukrainians, are a symbol of invincibility. A symbol that people in any country can become the best people on Earth at any moment."

The Russian forces charging toward Kyiv haven't made progress in the last day as they face Ukrainian resistance and low food and gas supply, a senior U.S. defense official told reporters Tuesday.

However, it could be a deliberate pause, the official said. "Part of the stall could be ... as a result of their own self-determined sort of pause in operations -- that they are possibly regrouping, rethinking, reevaluating," the official said.

The U.S. believes Russian forces "have committed now more than 80% of what was their pre-staged combat power," the official added.

The official said some Russian soldiers weren't told they were going into combat. The official said "not all of them were apparently fully trained and prepared."

The strong Ukrainian resistance has also hurt morale, according to the official.

Russia has now launched more than 400 missiles on Ukraine, the official said. The U.S. believes Russia has launchers that could be used for thermobaric weapons, but cannot confirm their use, the official said.

Russian forces are making the most progress in the south. Russians are attacking Kherson in south Ukraine, which "appears very much to be contested city at this point," the official said.

Russians are also approaching Mariupol in southeastern Ukraine, and while they haven't yet entered the city, "they are close enough now that they could attack Mariupol with long range fires," the official said.

Two towns on the path to Mariupol are believed to be occupied by the Russians, according to the official.

The U.S. believes the Russians hope to move north out of Mariupol up to the heavily-contested city of Kharkiv. The official said they believe Russian forces are trying to encircle Kharkiv.

The U.S. official noted that they've seen "certain risk-averse behavior by the Russian military" over the last week.

"Take the amphibious assault, for instance. They put those troops ashore a good 70 kilometers away from Mariupol because they knew Mariupol was going to be defended and they could put them ashore in an uncontested environment. And they still haven't reached Mariupol," the official said.

"They are not necessarily willing to take high risks with their own aircraft and their own pilots," the official said.

"And of course we're seeing that on the ground -- the fairly slow and steady progress that they have made, and you guys are seeing it for yourselves on the ground where ... units are surrendering, sometimes without a fight."

-ABC News' Matt Seyler