Washington (CNN) — US Vice President Kamala Harris on Friday called reports Russian opposition leader Alexei Navalny has died in a Russian prison “terrible news,” and that “Russia is responsible.”

“We’ve all just received reports that Alexey Navalny has died in Russia. This is, of course, terrible news, which we are working to confirm,” Harris said as she began her remarks.

She added, “If confirmed this, would be a further sign of Putin’s brutality. Whatever story they tell, let us be clear: Russia is responsible.”

The Russian prison service said Friday morning that Navalny died. He had been serving multiple lengthy prison sentences for crimes that he had denied. He faced those charges after returning to Russia following treatment in Germany after being poisoned in August 2020. Navalny returned to Russia after that treatment concluded in 2021, and he was quickly arrested.

Navalny had long been a point of contention between the US and Russia. President Joe Biden previously told reporters in 2021 that he warned Russian President Vladimir Putin that the consequences would be “devastating for Russia,” if Navalny died in prison.

Harris had been facing the fraught task of reassuring US allies on the world stage, as lawmakers struggle to pass aid for Ukraine and Israel and former President Donald Trump threatens to abandon NATO allies.

It was another high-profile moment for Harris to address the Munich Security Conference Friday amid a consequential moment in US foreign policy, as ongoing conflicts overseas have roiled domestic politics. It came at a delicate time for the White House, which continues to grapple with the fallout of the special counsel report that called into question President Joe Biden’s mental acuity and has placed renewed focus on the vice president.

But it suddenly became an opportunity for Harris to be the most prominent American voice to offer a reaction to the reports of Navalny’s death.

National security adviser Jake Sullivan said on NPR earlier Friday that the US was working to confirm Navalny’s death.

“If it’s confirmed, it is a terrible tragedy, and given the Russian government’s long and sordid history of doing harm to its opponents, it raises real and obvious questions about what happened here,” Sullivan said.

The administration had repeatedly called for Navalny’s immediate release, and CNN has reported Biden called for Navalny’s release in his first phone call with Putin after taking office in 2021.

After her opening comment on Navalny, Harris transitioned into her prepared remarks that were meant to reassure American allies over the future of US foreign policy.

Chief among the worries from the US’ top allies is Trump’s statement last weekend that he would encourage Russia to do “whatever the hell they want” to any NATO member country that doesn’t meet spending guidelines on defense.

After the Biden administration helped strengthen the bonds of the NATO alliance following Russia’s invasion of Ukraine, Trump’s statement is sparking real concern that he would not abide by the collective-defense clause at the heart of the alliance if reelected.

Concern is also rising over the ability of Washington to send more aid to Ukraine. For months, the White House’s national security supplemental request that includes billions in funding for Ukraine and Israel, among other priorities, has remained stalled in Congress over GOP infighting.

Against that backdrop, White House officials have repeatedly warned of the dangers of ceding ground to Russia. Harris is expected to lean into that message Friday and draw a sharp contrast from Trump’s foreign policy approach.

“The Vice President will recommit to defeat the failed ideologies of isolationism, authoritarianism, and unilateralism, which, she will argue, will would only weaken America,” a White House official told CNN.

“She will denounce these approaches to foreign policy as short-sighted, dangerous, and destabilizing. She will argue that they could lead to a world of disorder – to the detriment of the American people and the world,” the official added.

It’s a message that has been promoted by her boss this week. Biden took direct aim at his predecessor on Tuesday for saying he would encourage Russia to invade countries who don’t meet their NATO obligations, pointedly accusing Trump of “bowing down” to Vladimir Putin in some of his harshest criticism of his likely rival on foreign policy to date.

Trump, Biden claimed, sent a “dangerous and shocking” signal with his comments, delivered during a weekend campaign rally.

“Can you imagine a former president of the United States saying that?” Biden asked from the State Dining Room. “The whole world heard it. The worst thing is he means it.”

“No other president in our history has bowed down to a Russian dictator,” Biden went on. “Let me say this as clearly as I can: I never will. For God’s sake, it’s dumb. It’s shameful. It’s dangerous. It’s un-American.”

Trump’s comment had drawn immediate consternation, not only from the American foreign policy establishment but from American NATO allies, who have watched warily as Russia proceeds with its invasion of Ukraine. The former president on Wednesday said he wouldn’t defend NATO nations who don’t spend enough on defense but did not repeat his comment about encouraging Russia to do whatever they wanted.

“I’ve been saying look, if they’re not going to pay, we’re not going to protect, OK. And Biden said, ‘Oh this is so bad, this is so terrible that he would say that.’ No, if they’re not paying their bills, and most of them weren’t when I got there,” Trump said at a campaign event in North Charleston, South Carolina.

The White House has repeatedly stressed the need to deliver additional funds to Ukraine, framing it as a matter of national security. Harris will meet with Ukrainian President Volodymyr Zelensky on Saturday.

On Tuesday, Biden spent a significant portion of his speech on Ukraine aid going after Trump for the remark, which he said undercut longstanding US values.

In a speech that mentioned Trump by name at least a half-dozen times, sought to forcefully rebut questions about American commitment to its allies.

“When America gives us word, it means something. When we make a commitment, we keep it and NATO is a sacred commitment,” Biden said.

“Donald Trump looks at this as if it’s a burden,” he added.

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