Russia-Ukraine updates: US sanctions Russian military shipbuilder, diamond miner

Russian and Ukrainian negotiators continued peace talks virtually on Friday, Mykhailo Podolyak, a chief negotiator for the Ukrainians, told ABC News.

"On the table is the key document proposed by the Ukrainian delegation - the Treaty on Security Guarantees," Podolyak said. This proposed agreement provides for the possibility of exit from the war and the prevention of future conflicts.

Ukraine proposed a new system of security guarantees similar to NATO's collective defense clause which would legally require "guarantor countries" to provide arms and impose a "no-fly" zone over Ukraine, in the event of an attack.

Both sides are working on the legal wording of the basic provisions of the contract, Podolyak said.

"The discussion is extremely difficult, since the negotiating positions of the parties are strongly influenced by the daily change in the military situation on all lines of contact," Podolyak said.

-ABC News' Bruno Roeber and James Longman

An International Committee of the Red Cross team that was on its way to Mariupol to facilitate the safe passage of civilians on Friday had to return to Zaporizhzhia. The ICRC said arrangements and conditions made it impossible to proceed.

The ICRC team, which consists of three vehicles and nine personnel, said it will try again on Saturday.

The ICRC said it is critical that parties respect the agreements and provide the necessary conditions and security guarantees, and that it plans to accompany the convoy out of Mariupol to another Ukrainian city.

-ABC News' Cindy Smith

The International Atomic Energy Agency, the United Nations' nuclear watchdog, said on Friday that radiation around the Chernobyl nuclear power plant is normal.

"General radiation around the plant is quite normal," IAEA Director General Rafael Mariano Grossi said at a press conference.

There have been instances of relatively higher levels of localized radiation, which may have been caused by heavy vehicles moving in the area, the IAEA said.

The IAEA said it does not have any evidence that people were possibly contaminated.

Russia has not discussed its withdrawal from Chernobyl with the IAEA, the organization said.

"On the issue of radiation we are in consultation with the Ukrainian side," Grossi said.

Grossi repeatedly stressed the unpredictability of working in a war zone, saying things may not have gone strictly according to plan.

"In case there was an emergency taking place, we are setting up a mechanism whereby we can send a team to assist almost immediately," Grossi said.

-ABC News' Guy Davies

The International Committee of the Red Cross is leading a large convoy on Friday to help civilians escape the hellscape that has become of Ukraine's besieged port city of Mariupol, according to Crystal Wells, a spokesperson for the Geneva-based humanitarian organization.

"This effort has been and remains extremely complex," Wells told ABC News in a statement. "There are a lot of moving parts and not all the details are yet in place to ensure that this happens in a safe manner today. We remain hopeful, we are in action moving toward Mariupol, but it’s not yet clear that this will happen today."

According to Wells, the three ICRC vehicles, carrying nine ICRC staff, are leading vehicles from other organizations -- "potentially 54 buses." Images circulating on social media show other civilian vehicles joining the convoy.

"Our presence puts a humanitarian marker on this movement of people, giving the convoy additional protection and reminding all sides of the civilian, non-military, humanitarian nature of the operation," Wells said. "If and when it does happen, the ICRC's role as a neutral intermediary will be to lead the convoy out from Mariupol to another city in Ukraine. We’re unable to confirm which city at the moment as this is something the parties must agree to."

The situation in Mariupol "is horrendous and deteriorating, and it’s now a humanitarian imperative that people be allowed to leave, and aid supplies be allowed in," according to Wells.

"We're running out of adjectives to describe the horrors that residents in Mariupol have suffered," she added. "The people of Mariupol have suffered weeks of heavy fighting, with dwindling water, food and medical supplies."

The ICRC has had "open communication channels" with both Ukraine and Russia, Wells said, "but ensuring that all the details are agreed upon and well understood by all sides, and then communicated down the chain of command, and to the residents of Mariupol, is a challenge, and one that continues to take time to sort out."

"The details that we insist are cemented in place include the exact safe passage route, its exact start time, and its duration," she noted. "We have to be certain that a cease-fire holds. We have to be certain that this humanitarian convoy can safely move through military checkpoints."

-ABC News' Brian Hartman