US President Joe Biden's debut on TikTok has caused a stir -- not least because the Chinese-owned social media platform is still officially considered a security risk by Washington.

The video posted during the Super Bowl on Sunday was part of an effort by the 81-year-old's reelection campaign to reach younger voters, and included a reference to the quirky meme of a laser-eyed Biden alter-ego.

But Republicans have criticized Democrat Biden for using an app that is banned on US federal government devices over fears it harvests data for Beijing.

Even the White House admitted it still had concerns about TikTok on Monday. 

"There are still national security concerns about the use of Tiktok on government devices and there's been no change to that policy," National Security Council spokesman John Kirby told reporters after repeated questions about the issue.

The White House said that election rules barred it from formally commenting on campaign matters, but said more broadly that it was aware of fears that platforms like TikTok could spread disinformation.

"It's a concern that we have," said White House Press Secretary Karine Jean-Pierre.

TikTok is owned by Chinese firm ByteDance and has been accused by a wide swath of US politicians of being a propaganda tool used by Beijing, something the company furiously denies.

The concerns "didn't stop the Biden campaign from joining the CCP's dangerous propaganda app," Republican Senator Joni Ernst said on X, formerly Twitter, referring to the Chinese Communist Party.

"Panic is when the Biden campaign joins TikTok after the White House banned the app from devices a year ago," added Republican Representative Darrell Issa.

'hey guys'

Nevertheless, Biden's campaign has clearly decided that engaging on TikTok is worth it to win over younger voters ahead of a likely November clash with Republican former president -- and social media juggernaut -- Donald Trump.

They are also counting on such social media posts to allay voter concerns over Biden's age, which have mounted since a special counsel report last week described him as a "well-meaning, elderly man with a poor memory."

Titled "lol hey guys," Sunday's video posted on the @bidenhq campaign account touches light-heartedly on topics ranging from politics to the NFL championship game.

"I'd get in trouble if I told you," Biden jokes when asked about a right-wing conspiracy theory that the game had been rigged so pop star Taylor Swift -- who is dating Kansas City Chiefs star Travis Kelce -- could use her fame to endorse Biden.

The video then flashes up the "Dark Brandon" meme, an image of Biden with glowing red eyes and a big grin that Democrats use to imply super-powers.

"The President's TikTok debut last night -- with more than 5 million views and counting -- is proof positive of both our commitment and success in finding new, innovative ways to reach voters," Biden campaign deputy manager Rob Flaherty said in a statement.

Jean-Pierre said this exploration of new media partly explained why Biden has held fewer press conferences than his predecessors -- 33 in his first three years, compared with Barack Obama's 66 and Trump's 52 in the same time span, according to the University of California Santa Barbara's American Presidency Project.