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 (Russian President Vladimir) 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 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.

During her speech, Harris launched a veiled attack against Trump, describing his foreign policy approach as “dangerous” and issuing a stark warning if the US cedes ground to Russia.

“They suggest it’s in the best interest of the American people to isolate ourselves from the world, to flout common understandings among nations, to embrace dictators, and adopt the repressive tactics and abandon commitments to our allies in favor of unilateral action,” Harris said.

“Let me be clear – that worldview is dangerous, destabilizing and indeed shortsighted,” she said.

Trump had drawn immediate consternation last weekend for saying he would encourage Russia to invade countries who don’t meet their NATO obligations. The comment concerned not only 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 wante

“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.

Harris maintained Friday that US commitment to NATO remains “ironclad” in the wake of Trump’s comments.

It’s a similar message to the one that has been promoted by her boss this week. Biden took direct aim at his predecessor on Tuesday, pointedly accusing Trump of “bowing down” to 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.

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.

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.

Harris called Putin’s war in Ukraine an “utter failure” and stressed the consequences of ceding any ground to Russia, reaffirming US support for Ukraine.

“Imagine if America turned our back on Ukraine and abandoned our NATO allies and abandoned our treaty commitments. Imagine if we went easy on Putin. Let alone encouraged him,” Harris said.

“History offers a clue. If we stand by while an aggressor invades its neighbor with impunity, they will keep going. In the case of Putin, that means all of Europe would be threatened. If we fail to impose severe consequences on Russia, other authoritarians across the globe would be emboldened,” Harris said.

This story has been updated with additional developments on Friday