Russia-Ukraine updates: Putin suspends key US-Russia nuclear treaty in speech denouncing West

Ukraine's Zaporizhzhya Nuclear Power Plant has lost connection to its last remaining main external power line, the International Atomic Energy Agency said in a statement Saturday.

Zaporizhzhya is continuing to supply electricity to the grid through a reserve line, the IAEA said it was informed while at the site.

Three other power lines were lost earlier during the conflict, the IAEA said.

The information came less than 48 hours after IAEA Director General Mariano Grossi established a presence in the plant.

One reactor is still operating and producing electricity both for cooling and other essential safety functions at the site and for households, factories and others through the grid, the IAEA said.

The power plant has been held by Russian forces since early March, but its Ukrainian staff are continuing to operate the plant.

The head of the United Nations' nuclear watchdog said the situation at the Zaporizhzhia nuclear power plant remains "extremely complex and challenging."

International Atomic Energy Agency Director General Rafael Grossi, who just returned from leading a team of over a dozen experts sent to inspect the besieged plant, said during a briefing Friday that the physical integrity of the building "has been violated not once, but several times," and that the integrity of the power supply to the plant is a major concern.

Grossi said he asked to talk to the Russian military at the plant and "they were not available" and noted that his team was not allowed to access the power plant's "crisis center." He implied that the Russians are using it for some other purpose but that it does "not have an influence on the operation of the plant."

There are currently six IAEA experts at the plant, he said. Four of them are set to leave next week and two will stay for the foreseeable future.

-ABC News' Tom Soufi Burridge

A major pipeline that supplies natural gas from Russia to Europe will be indefinitely shut off, Russian energy corporation Gazprom said Friday.

Gas supplies via the Nord Stream pipeline have been suspended since Wednesday for maintenance of its only operative gas compressor unit, Gazprom said. The company was planning to restart the flow of natural gas on Saturday barring any issues.

An oil leakage was detected during the scheduled maintenance and gas transmission "has been fully shut down until the operational defects in the equipment are eliminated," Gazprom said. The company did not give a timeline on the restart.

The shutdown marks Russia's latest supply cutback to Europe following its invasion of Ukraine, as Europe faces an energy crisis.

Several experts with the United Nations' nuclear watchdog have left the Zaporizhzhia power plant, according to Russian news agency Interfax.

Four out of the nine vehicles that arrived earlier Thursday as part of the International Atomic Energy Agency convoy left at 2:15 p.m. local time after about four hours at the plant, according to an Interfax reporter on the ground at the Ukrainian facility.

IAEA Director General Rafael Grossi, who is leading the mission, was among those to leave, while some experts remained behind and will stay at the plant, according to Interfax.

Ukraine's nuclear regulator, Energoatom, also confirmed Thursday that the majority of the IAEA mission has left the power plant, including Grossi, and that five experts stayed behind to unload equipment brought to the plant.

The IAEA team is expected to remain at the plant through Sept. 3, Energoatom said in an update posted to Telegram.

In a video statement posted to Twitter, Grossi said he completed a first tour of "key areas" at the plant on Thursday.

"Of course there's a lot more to do," he said. "My team is staying on, and more importantly and most importantly, we are establishing a continued presence ... from the IAEA here."

-ABC News' Natalia Shumskaia and Fidel Pavlenko