A manipulated video of Ukrainian President Volodymyr Zelenskyy calling on citizens to surrender to Russia has been shared online.
The false video appears to show Zelenskyy addressing the nation and encouraging citizens to "lay down arms".
One version of the "deepfake" was viewed more than 120,000 times on Twitter.
Zelenskyy's face and voice have been edited onto the video using artificial intelligence (AI) to create the deepfake video.
The viral clip differs from the majority of misinformation that has been shared since Russia invaded Ukraine on February 24.
Most false rumours originate from images or videos that have been taken out of context, from other wars or world events.
"This is the first deepfake that we've seen used in an intentional and broadly deceptive way," said Sam Gregory, programme director at Witness, a human rights and technology group.
"It's not an effective deepfake, partly because it's not an extremely well-made deepfake, but also because Ukraine has done a masterful job pre-bunking and then swiftly rebutting the video."
"Deepfakes haven't been the main problem in Russia's invasion of Ukraine," Gregory told Euronews.
Earlier this month, Ukraine's Land Forces warned citizens to be aware of potential manipulated videos that could show apparent calls to surrender.
"Videos made through such technologies are almost impossible to distinguish from the real ones," the authority said in a Facebook post.
"[The] goal is to disorient, sow panic, disbelieve citizens and incite our troops to retreat. Rest assured - Ukraine will not capitulate."
On Wednesday, Ukraine's President swiftly released a video on his own Instagram page, where he denied making any such statement.
"The only ones who should give up arms are Russian soldiers,” Zelenskyy said.
A deepfake video of Russian President Vladimir Putin also appeared online on Wednesday, seemingly created in retaliation to the fake Zelenskyy clip. One version on Twitter had more 50,000 views
In the video, the Russian president appears to announce the surrender of Russia and calls on soldiers to "go home while you're alive".
The video has also been manipulated using AI from a recent national address by Putin.
Ukrainian news channels Ukraine 24 and Today, whose live broadcasts were hacked to promote the same "surrender" message as the fake video, also released statements echoing the words of their President.
Sam Gregory told Euronews that Ukraine's efforts to pre-empt manipulated videos of Zelenskyy was a "really appropriate strategy".
"This is the first time we have seen a really significant perceived threat of deepfakes that can be anticipated in a conflict," he said.
"I think it provides a model that is applicable in some scenarios globally to politicians, pre-bunking and then a rapid response."
Witness has been working to help online users understand trusted videos of the Ukraine conflict and has been calling on social media platforms to provide more open guidance and tools.
In a statement, the head of security policy at Meta confirmed that had removed the deepfake video of President Zelenskyy.
"We've quickly reviewed and removed this video for violating our policy against misleading manipulated media, and notified our peers at other platforms," said Nathaniel Gleicher.