Tuesday's talks in Istanbul between Ukraine and Russia have concluded.

Russian delegation head Vladimir Medinsky told reporters the talks were "constructive."

Meanwhile, Alexander Chaly of the Ukrainian delegation told reporters that talks will continue, and in two weeks they plan to involve other countries in the negotiation process.

Ukrainian negotiator David Arakhamia said he believes enough has been covered to now involve the presidents of Ukraine and Russia in the talks.

Medinsky noted, "As a result of today's substantive conversation, we have approved and offer a solution, according to which a meeting between the heads of state is possible simultaneously with the initialing of the agreement."

"The proposed format is like this: first an agreement will be drafted, then the agreement will be approved by the negotiators and signed by the foreign ministers at a meeting, and then the possibility of a meeting between the heads of state will be discussed in order to sign this agreement," Medinsky said.

Ukrainian officials said a military alliance of other countries -- including the U.S. -- needs to be created to provide security protections to Ukraine.

U.S. Secretary of State Antony Blinken expressed skepticism about the talks, saying he would leave it to the Ukrainians to characterize any progress.

Russia's military will "drastically" decrease activity near Kyiv and Chernihiv to try to improve trust and aid further talks with Ukraine, Russian Deputy Defense Minister Col. Gen. Alexander Fomin said Tuesday.

"Due to the fact that the negotiations on elaborating a treaty on Ukraine's neutrality and nuclear-free status, as well as on providing Ukraine with security guarantees are shifting to the practical field, and taking into account the principles discussed during today's meeting," Fomin told reporters, "the Russian Defense Ministry has decided to decrease its military activity in the areas of Kyiv and Chernihiv drastically in order to increase mutual trust and create conditions required for further negotiations and for achieving the ultimate goal of reaching an agreement on and signing of the aforementioned treaty."

U.S. Secretary of State Antony Blinken was asked by reporters Tuesday about Russia's announcement that it will scale back operations around Kyiv and Chernihiv. He said it may be a "means by which Russia is, once again, trying to deflect and deceive people into thinking that it's not doing what it is doing, whether it's simply trying to regroup given the heavy losses that it's suffered -- I don't know." But any attempt to "subjugate" eastern or southern Ukraine will not succeed either, he added.

President Joe Biden will hold a call at 9:15am ET Tuesday with French President Emmanuel Macron, German Chancellor Olaf Scholz, Italian Prime Minister Mario Draghi and United Kingdom Prime Minister Boris Johnson to discuss the latest with Russia’s invasion of Ukraine, according to the White House.

Macron is also set to speak with Russian President Vladimir Putin on Tuesday.

-ABC News' Justin Ryan Gomez

More than 3.9 million people have been forced to flee Ukraine since Russian forces invaded on Feb. 24, according to the latest figures from the United Nations Refugee Agency.

The tally from the U.N. High Commissioner for Refugees (UNHCR) amounts to just over 8.8% of Ukraine's population -- which the World Bank counted at 44 million at the end of 2020 -- on the move across borders in 34 days.

More than half of the refugees crossed into neighboring Poland, UNHCR figures show.

-ABC News' Zoe Magee

All Russian troops have left the Ukrainian cities of Kyiv and Chernihiv, withdrawing north toward the borders of Belarus and Russia to consolidate before likely redeploying to the Donbas region in eastern Ukraine, a senior U.S. defense official told reporters Wednesday.

But even with the Russians gone, the territory remains treacherous.

"There are some indications that they left behind mines and things like that, so the Ukrainians are being somewhat careful in some areas north of Kyiv as they begin to clear the ground and clear the territory and re-occupy it," the official said.

While the U.S. hasn't yet seen these troops redeploy elsewhere in Ukraine, it'll likely happen soon, according to the official. Ukrainian forces are preparing for a major fight in Donbas, the official said.

The official also said the Pentagon is "monitoring" an apparent nitric acid explosion in Ukraine's Luhansk region, which Russia blamed on Ukraine.

"We've seen the Russians claim that this was a Ukrainian attack on this. We do not believe that is true," the official said. "We do believe that the Russians are responsible, but exactly what they used when they did it, why they did it, what the damage is, we just don't have that level of detail," the official said.

The official also noted that a small number of Ukrainians currently in the U.S. for "professional military education" were pulled aside for a couple days of training on Switchblade drones, which the U.S. is sending overseas as part of its military aid, according to the official.

"Although it's not a very difficult system to operate, we took advantage of having them in the country to give them some rudimentary training on that," the official said.

-ABC News' Matt Seyler