The shelling by Russia in recent days around the Zaporizhzhia nuclear power plant in Ukraine landed close to two of the facility's nuclear reactor buildings, according to the International Atomic Energy Agency.

Rafael Mariano Grossi, director general of the IAEA, said Sunday that Russian rockets hit two "special buildings" about 100 meters, or less than 330 feet, from the nuclear reactor buildings.

Citing a report from Ukrainian officials, Grossi said the buildings hit in the attack house the facility's water treatment plants, equipment repair shops or waste management facilities.

Grossi said there was damage to some water pipelines at the site but they have since been repaired. He said measurements of radioactivity were within normal range and there was no indication of any hydrogen leakage.

He said the nuclear plant, the largest in Europe, continues to access electricity from an off-site source after the plant temporarily lost connection to its last remaining operational 750 kilovolt external power line on Thursday.

Two reactor units that were disconnected from the electricity grid when power was cut to the plant on Thursday have been re-connected, Grossi said. The other four reactor units that were disconnected before Thursday remained shut down on Sunday.

He said the latest shelling once again underlines the risk of a potential nuclear accident at the Zaporizhzhia plant, which is under the control of Russian forces but being operated by Ukrainian staff.

-ABC News' Christine Theodorou

International Atomic Energy Agency director general Rafael Mariano Grossi said he’s engaged in active consultations with all parties to lead and organize an IAEA mission to the Zaporizhzhia nuclear power plant "hopefully in the next few days.” Grossi said in a statement that Thursday’s sudden loss of external power showed that IAEA's presence is urgently needed.

-ABC News' Alex Faul

The head of Ukraine’s nuclear agency, Petro Kotin, called Thursday’s disconnection of power lines at Zaporizhzhia, Europe’s largest nuclear power plant, a "very serious deterioration… due to Russian shelling on the side of Nikopol on the side of the Dnipro river."

The diesel generator operators were able to kick in during the disconnection, Kotin told ABC News on Friday.

Asked what’s the likelihood this would happen again, Kotin said, "This is one step from the emergency radiation, actually. Diesel is just the last defense, if you actually lose the diesel stuff, you already have radiation, and it's out of the territory of the plant."

He said there'd be 10 days of idle time before a meltdown if the diesel generators are working. If all diesel generators are down, it could be 1.5 hours.

Inspectors could gain access to the site in as soon as five days, he said.

For Russia, the Zaporizhzhia plant is a strategic stronghold as it seeks to control the ground pathway from occupied Donetsk to Crimea and onto Odesa.

Zaporizhzhia supplies Ukraine with around 20% of its energy.

Kotin reiterated that Russia intends to switch power to Russian-controlled areas.

-ABC News' Britt Clennett, Dada Jovanovic and Yuri Zalizniak

All of the reactors at Zaporizhzhia nuclear power plant, where shelling has been ongoing, have been shut down for the first time in the plant’s history, Ukraine's state nuclear regulator Energoatom reported.

Zaporizhzhia -- the largest nuclear power plant in Europe -- has six reactors, two of which are active, according to Ukraine's state nuclear regulator, Energoatom. At 12:12 p.m. local time, the last operating line providing power to the plant was disconnected due to hostilities in the area, and as a result all six reactors were disconnected from the grid for 17 minutes, Energoatom said.

At 12:29 p.m. local time the overhead line was restored and reactors Nos. 5 and 6 start operating again.

At 2:14 p.m. local time, the overhead line was disconnected again, shutting down reactor No. 6 and leaving only reactor No. 5 operating. Work is underway to reconnect No. 6 to the grid.

The International Atomic Energy Agency said the temporary shut down further shows "the urgent need for an IAEA expert mission to travel to the facility."

If external power is lost there's not active circulation of the water that cools the reactor and that could lead to a reactor meltdown. However, the plant "remained connected to a 330 kV line from the nearby thermal power facility that can provide back-up electricity if needed," the IAEA said in a statement. "As a result of the cuts in the 750 kV power line, the ZNPP’s two operating reactor units were disconnected from the electricity grid and their emergency protection systems were triggered, while all safety systems remained operational."

"There was no information immediately available on the direct cause of the power cuts," the IAEA said. "The six-reactor ZNPP normally has four external power lines, but three of them were lost earlier during the conflict. The IAEA remains in close contact with Ukraine and will provide updated information as soon as it becomes available."

Ukrainian President Volodymyr Zelenskyy warned Thursday, "The world must understand what a threat this is: If the diesel generators hadn’t turned on, if the automation and our staff of the plant had not reacted after the blackout, then we would already be forced to overcome the consequences of the radiation accident. Russia has put Ukraine and all Europeans in a situation one step away from a radiation disaster."

He called on the IAEA and other international organizations to act faster, "because every minute the Russian troops stay at the nuclear power plant is a risk of a global radiation disaster."

-ABC News' Christine Theodorou, Fidel Pavlenko and Natalia Shumskaia

Russian forces will "now almost certainly" switch focus to capturing Donetsk Oblast after claiming control of neighboring Luhansk Oblast in eastern Ukraine's disputed Donbas region, according to intelligence briefings from the U.K. Ministry of Defense.

Russian President Vladimir Putin declared victory in Luhansk on Monday, a day after Ukrainian troops withdrew from the city of Lysychansk -- their last stronghold of resistance in the province. Ukrainian troops had spent weeks trying to defend Lysychansk and to keep it from falling to Russian forces, as the neighboring city of Sievierodonetsk did a week ago. A river separates the two cities.

"Russia's focus will now almost certainly switch to capturing Donetsk Oblast, a large portion of which remain under the control of Ukrainian forces," the U.K. Ministry of Defense said in Monday's briefing. "The fight for the Donbas has been grinding and attritional and this is highly unlikely to change in the coming weeks."

Putin has made capturing the entire Donbas -- Ukraine's mostly Russian-speaking industrial heartland in the east -- a key goal in his war in neighboring Ukraine. Russia-backed separatists in Donbas have battled Ukrainian forces since 2014, when they declared independence from Kyiv after the Russian annexation of Ukraine's Crimean Peninsula. Moscow formally recognized the self-proclaimed republics in Luhansk and Donetsk oblasts just days before launching its Feb. 24 invasion.

"Russia's relatively rapid capture of Lysychansk extends its control across virtually all of the territory of Luhansk Oblast, allowing it to claim substantive progress against the policy objective it presented as the immediate purpose of the war, namely 'liberating' the Donbas," the U.K. Ministry of Defense said in Tuesday's briefing.

"Ukrainian forces have likely largely withdrawn in good order, in line with existing plans," the ministry continued. "The Ukrainian held areas of Sieverodonetsk-Lyschansk consisted of a bulge or salient which Russian could attack from three sides. There is a realistic possibility that Ukrainian forces will now be able to fall back to a more readily defendable, straightened front line."

"The battle for the Donbas has been characterised by slow rates of advance and Russia’s massed employment of artillery, levelling towns and cities in the process," the ministry added. "The fighting in Donetsk Oblast will almost certainly continue in this manner."