The legislation gives TikTok nine months to divest from its Chinese parent company ByteDance or be shut out of the American market.

US and other Western officials have alleged the social media platform allows Beijing to collect data and spy on users. It has 170 million users in the United States alone, many of them young.

Critics say TikTok is also a conduit to spread propaganda. China and the company strongly deny the claims.

"Make no mistake, this is a ban. A ban on TikTok and a ban on you and your voice," TikTok boss Shou Zi Chew said in a video posted on TikTok moments after President Joe Biden signed the bill into law.

"Politicians may say otherwise, but don't get confused. Many who sponsored the bill admit a Tiktok ban is the ultimate goal."

Chew called the move "ironic" given that the "freedom of expression on TikTok reflects the same American values that make the United States a beacon of freedom."

"Rest assured, we aren't going anywhere," Chew told the platform's users.

"We will keep fighting for your rights in the courts. The facts and the Constitution are on our side."

The ban measure was included in a $95 billion foreign aid package, including military assistance to Ukraine, Israel and Taiwan.

The bill, which could trigger the rare step of barring a company from operating in the US market, passed the Senate by a 79-18 vote three days after it cleared the House of Representatives with strong bipartisan support.

Ahead of the vote, FBI Director Christopher Wray said that TikTok parent company ByteDance is "beholden to the Chinese government" which is "attempting to steal our AI and hack American technology every day."

Americans must think of TikTok's "power, access, capability, control" as being in the hands of the Chinese government and intelligence service, Wray said.

Under the bill, ByteDance would have to sell the app or be excluded from Apple and Google's app stores in the United States.

According to Wedbush analyst Dan Ives, likely buyers for TikTok would be Microsoft or Oracle.

TikTok for years has been in the crosshairs of American authorities, who say the platform allows Beijing to snoop on users in the United States.

The bill passed by Congress also gives the US president the authority to designate other applications as a threat to national security if they are controlled by a country deemed hostile.

Elon Musk, the billionaire owner of X, formerly Twitter, came out last week against banning TikTok, saying "doing so would be contrary to freedom of speech and expression."