Russian President Vladimir Putin offered his first comments Thursday on the plane crash that presumably killed Wagner Group head Yevgeny Prigozhin and the private military company's co-founder Dmitry Utkin along with eight others near Kuzhenkino, Russia, on Wednesday.

"As for the aviation tragedy, first of all, I want to express my sincerest condolences to the families of all the victims," Putin said in an on-camera address, adding that Wagner Group made a "significant contribution to our common cause of fighting the neo-Nazi regime in Ukraine."

"I knew (Yevgeny) Prigozhin for a very long time, since the early 1990s. He was a man with a complex destiny, and he made serious mistakes in life," Putin said. "He achieved the results he needed both for himself and, when I asked him, for the common cause, as in these last months."

Putin said of the investigation, "But what is absolutely clear -- the head of the Investigative Committee reported to me this morning, they have already launched a preliminary investigation into this incident. And it will be carried out in full and to the end. There is no doubt about that here. Let's see what the investigators say in the near future. Tests -- technical and genetic tests -- are being carried out now. This takes some time."

-ABC News’ Will Gretsky

Mercenaries with the Russian private military company Wagner Group were observed leaving Belarus where the group’s forces had set up camp since a failed rebellion against Russian military leaders in June, according to Andrii Demchenko, a spokesman for Ukraine’s State Border Guard Service.

The group’s movements were observed by Ukrainian border guards and intelligence officials, Demchenko said Thursday.

The reported exit comes a day after Wagner leader Yvegeny Prigozhin and the group’s co-founder and operations manager Dmitry Utkin were presumed to have died in a plane crash near Moscow.

-ABC News’ Will Gretsky

Ukrainian troops have landed in occupied Crimea, a state defense official said on Thursday.

The landing in territory long held by Russian forces was accomplished without Ukrainian casualties, Andriy Yusov, spokesperson for the Defense Ministry, said on Telegram. Russian forces suffered personnel losses, he said.

Russia illegally annexed Crimea from Ukraine in 2014.

-ABC News’ Joe Simonetti

Ukrainian President Volodymyr Zelenskyy spoke out against American critics who are pushing for cuts to military support to his country stating there are "dangerous voices" in Congress and in the U.S.

Zelenskyy told reporters Wednesday that his team was in constant contact with National Security Advisor Jake Sullivan and other U.S. national security officials, stating he was "glad" Ukraine had the backing of the White House, enjoyed bipartisan support in Congress and received “a lot” of support from the American public.

However, Zelenskyy said the coming year will be "very difficult," referring to the U.S. presidential election, which "will definitely have an impact on support for Ukraine."

"I think we’re going to have a hard time," Zelenskyy said.

He said the election results could be positive or negative for Ukraine.

“For our part, we will do everything to ensure that the support of the United States does not decrease…we will give all our time, our energy to constantly work with the USA," Zelenskyy said. “I expect that our partners in the United States will continue to be our partners and friends.”

Zelenskyy said Ukraine was working on lobbying Biden for longer range missiles.

-ABC News' Tom Buridge and Natalya Kushnir

Gen. Mark Milley, the U.S. military's top general, told reporters Friday that it's likely too early to tell the impact of the Wagner Group mutiny on Russian President Vladimir Putin.

"We want to know the answer to that question," Milley said when asked at the National Press Club if Yevgeny Prigozhin's mutiny had left Putin weakened. "I don't think we have evidence, conclusive evidence, either way, yet too early to tell."

Milley acknowledged that Ukraine's counteroffensive is making steady progress, but moving slowly -- something he said was not surprising given how tough of a fight it is.

"At the end of the day, Ukrainian soldiers are assaulting through minefields and in the trenches, and this is literally a fight for their life. So yes, sure, it goes a little slow, but that is part of the nature of war," Milley said.

He also noted that the U.S. is considering sending cluster munitions to Ukraine, though no decision has been made.

-ABC News' Luis Martinez