Ukrainian soldiers were seen patrolling the streets of Irpin on Tuesday, following claims that the besieged Kyiv suburb has been "liberated" from Russian forces.

Video released by the Ukrainian military and verified by ABC News shows their troops driving through Irpin, a northwestern suburb of Kyiv where some of the heaviest fighting near the Ukrainian capital has taken place.

Irpin Mayor Oleksandr Markushyn announced in a video posted to Telegram on Monday that "Irpin has been liberated."

Meanwhile, the Ukrainian government released video on Tuesday showing elderly people who had been evacuated from Irpin arriving in Kyiv, where they reunited with their families.

The footage purportedly shows 86-year-old Irpin resident Olga Molchanova being embraced by her daughter and son. Molchanova's adult children had evacuated Irpin earlier via a humanitarian corridor, but their parents refused to leave at the time, according to Ukraine's Center for Strategic Communication and Information Security (Stratcom).

"Recaptured by Ukrainian army, Irpin remains too dangerous for civilians to stay," Stratcom said in a post on Twitter alongside the video.

-ABC News' Monica Camacho and Fergal Gallagher

Russian oligarch Roman Abramovich is taking part in Tuesday's in-person negotiations between Russian and Ukrainian delegations in Turkey's capital, a Turkish presidential source told ABC News.

Abramovich is the owner of the English professional football club Chelsea. The U.K. government has included him among the wealthy Russians targeted in recent sanctions.

The Wall Street Journal reported Monday, citing unnamed sources familiar with the matter, that Abramovich and two Ukrainian negotiators suffered symptoms of suspected poisoning after peace talks in Kyiv in early March.

A Turkish presidential source told ABC News that Abramovich suspected he was poisoned after experiencing eye problems.

Turkish officials confirmed there is a discussion regarding the food protocols during Tuesday's negotiations in Istanbul.

Ukraine is warning its delegation against eating or drinking while attending in-person peace talks with Russian negotiators, amid fears of potential poisoning.

"I advise to everyone who's going to any negotiations with Russia, not to eat or drink anything, and also not to touch any surfaces," Ukrainian Foreign Minister Dmytro Kuleba said in a statement Tuesday.

The warning came a day after The Wall Street Journal reported, , citing unnamed sources, that Russian oligarch Roman Abramovich and two Ukrainian negotiators had suffered symptoms of suspected poisoning following peace talks in Kyiv in early March.

-ABC News' Julia Drozd

The latest round of in-person peace negotiations between Russian and Ukrainian delegations kicked off in Istanbul on Tuesday morning, with Turkish President Recep Tayyip Erdogan in attendance.

Erdogan addressed both sides with a brief speech before the talks began.

"Establishing a cease-fire and peace as soon as possible will be to everyone's benefit. We think that we've entered a period where we need to achieve concrete results from negotiations," Erdogan said. "As members of the delegations, you've taken on a historic responsibility. The whole world is awaiting the good news that will come from you."

Footage showing the start of the meeting was broadcast by Russian state-backed television channel RT.

Tuesday's negotiations are taking place in Dolmabahce Palace in the Besiktas district of Turkey's capital, according to Turkish state-run news agency Anadolu Agency. It's the first face-to-face talks to take place between Russia and Ukraine in more than two weeks.

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