Russia has confirmed the use of thermobaric rockets, or vacuum bombs, the U.K. Ministry of Defense tweeted Wednesday.

The weapon uses a fuel container and two separate explosive charges to ignite a blast of extreme pressure and heat, creating a partial vacuum in an enclosed space.

The impact from the bomb is "devastating," according to the ministry.

-ABC News' Guy Davies

Papa John's and Heineken are the latest brands to cease business in Russia in response to the invasion of Ukraine.

The American pizza chain and the Dutch beer company join internationally known brands such as McDonald's, The Coca-Cola Company, PepsiCo and Starbucks in suspending operations in Russia.

While Heineken has stopped the production and sale of beer in Russia, Papa John’s has suspended all corporate operations there as well.

"It has ceased all operational, marketing and business support to, and engagement with, the Russian market, where all restaurants are owned by independent franchisees, and a master franchisee who controls operations and provides all supplies and ingredients for the restaurants through a supply chain that it owns and operates," a statement released Wednesday by Papa John’s read.

-ABC News' Victor Ordonez

Russian forces severed the electricity to the Chernobyl nuclear power plant but there is "no immediate risk" of a radiation leak, International Atomic Energy Agency (IAEA) Director-General Rafael Mariano Grossi told ABC News in an interview Wednesday at the agency’s headquarters in Vienna.

There is active fuel at the site of the original reactors that melted down in 1986 but, for the time being, at least, there is enough capacity to cool spent nuclear fuel.

"There is no immediate risk in the dimensions that were imagined and there is work in progress to restore the electrical capacity," Mariano Grossi said. Still, he conceded, "It's a situation that is very fragile."

The lack of reliable electricity also impedes monitoring abilities, leaving the IAEA -- the nuclear watchdog of the United Nations -- occasionally blind to any spontaneous increase in radiation.

"We do have communications and then we lose. Then we recover it. It's not good in terms of following the safety, the security," Mariano Grossi said. "I'm concerned. I’m worried."

There are no IAEA inspectors on the ground while the fighting rages. The director-general said he would not send them in unless he can go first.

"I will not put my staff in harm’s way before me going first," Mariano Grossi said.

Russia is in control of Chernobyl and a second nuclear power station in Zaporizhia. For a time, neither plant had a way to exchange workers or upgrade staffing.

In Zaporizhia, Mariano Grossi said, a shift change is now happening. In Chernobyl, workers are not allowed off-site.

"We all need a break and especially people who are manning extremely sophisticated equipment. The stress is very high," he said.

Mariano Grossi is traveling Thursday to Turkey, where the Russian and Ukrainian foreign ministers will meet face-to-face for the first time since the two-week-old invasion began. He said he will ask each side to commit to "fundamentals," including respecting the physical security of each of Ukraine’s four nuclear power stations, plus Chernobyl.

"We haven't seen something as critical and worrying as a fire breaking out in a building adjacent to a nuclear reactor," Mariano Grossi said. "What really worries me is that unlike Fukushima (in Japan), where you had mother nature to blame, now it would be us."

-ABC News' Aaron Katersky and Robert Zepeda

House Minority Leader Kevin McCarthy broke with former President Donald Trump on Wednesday when he was asked whether he supported Trump's comments praising Putin as a "genius."

“I do not think anything is savvy or genius about Putin," McCarthy, R-Calif., said during a news conference. "I think Putin is evil, he is a dictator and I think he is murdering people right now."

On Feb. 23, a day before the start of the Russian invasion of Ukraine, Trump praised Putin and slammed his successor President Joe Biden in an appearance on a conservative talk radio program.

"This is genius. Putin declares a big portion of the Ukraine ... Putin declares it as independent. Oh, that's wonderful," Trump said of the Russian president's decision to recognize the two provinces of the Donbas Region of eastern Ukraine as independent republics and claimed rebels there asked him to send troops into Ukraine to protect them from Ukrainian military attacks.