WASHINGTON (NYTIMES) - The warning from the Pentagon was unequivocal: Military personnel should delete TikTok from all smartphones.

Now, a number of US military branches are heeding that advice, issued last month by the Defence Department, and have banned the popular Chinese-owned social media app on government-issued smartphones.

Some have even strongly discouraged members of the armed forces from keeping TikTok on their personal electronic devices.

The vigilance coincides with heightened scrutiny of the short-form video-sharing platform by Congress and a national security review of TikTok, which is among the top downloaded smartphone apps worldwide.

"Marine Corps Forces Cyberspace Command has blocked TikTok from government-issued mobile devices," Captain Christopher Harrison, a US Marine Corps spokesman, said on Friday (Jan 3) in an e-mail.

"This decision is consistent with our efforts to proactively address existing and emerging threats as we secure and defend our network. This block only applies to government-issued mobile devices."

In a Dec 16 message to the various military branches, the Pentagon said there was a "potential risk associated with using the TikTok app", and it advised employees to take several precautions to safeguard their personal information.

It said the easiest solution to prevent "unwanted actors" from getting access to that information was to remove the app.

"Doing so will not prevent already potentially compromised information from propagating, but it could keep additional information from being collected," the Pentagon's message said.

The US Army banned TikTok from military-issued smartphones in response to last month's warning, Lt Col Robin Ochoa, an Army spokeswoman, said on Friday in an e-mail.

"Those who have a government-issued device are requested to remove the application," she said.

Mr Josh Gartner, a spokesman for ByteDance, the Chinese parent company of TikTok, declined to comment about the Pentagon warning and the response of several military branches.

This was not the first time that the Defence Department had been compelled to urge members of the military to remove a popular app from their phones.

In 2016, the Defence Department banned Pokémon Go, the augmented-reality game, from military smartphones.

But in that case, military officials cited concerns over productivity and the potential distraction hazards of pursuing the virtual Pokémon while driving or walking. The Canadian military also grappled with Pokémon Go.

The concerns over TikTok centre on cyber security and spying by the Chinese government.

In a November blog post on TikTok's website, the general manager of TikTok US, Ms Vanessa Pappas, wrote that data security was a priority and that the company wanted to be as transparent as possible for stakeholders in the US.

The blog post came as the US government opened a national security review of a Chinese company's acquisition of the American company that became TikTok.

"As we have said before, and recently confirmed through an independent security audit, we store all US user data in the United States, with backup redundancy in Singapore," Ms Pappas wrote.

"TikTok's data centres are located entirely outside of China."

In October, Senators Chuck Schumer, a New York Democrat, and Tom Cotton, an Arkansas Republican, sent a letter to the acting director of national intelligence, Mr Joseph Maguire, calling for an assessment of national security risks posed by TikTok and other China-based content platforms.

The senators said Chinese companies must comply with a "vague patchwork" of intelligence, national security and cyber security laws that have no mechanism for appealing decisions of the Chinese communist government.

"Questions have also been raised regarding the potential for censorship or manipulation of certain content," the senators' letter said.

"TikTok reportedly censors materials deemed politically sensitive to the Chinese Communist Party, including content related to the recent Hong Kong protests, as well as references to Tiananmen Square, Tibetan and Taiwanese independence, and the treatment of Uighurs. The platform is also a potential target of foreign influence campaigns like those carried out during the 2016 election on US-based social media platforms."

Members of the US Air Force are not allowed to install unauthorised apps on their military-issued phones, an Air Force spokeswoman said on Friday in an e-mail.

The spokeswoman did not specify whether TikTok was one of those applications and did not immediately respond to a follow-up inquiry.

"The threats posed by social media are not unique to TikTok (though they may certainly be greater on that platform), and DoD personnel must be cautious when making any public or social media post," the Air Force spokeswoman said.

"All DoD personnel take annual cyber-awareness training that covers the threats that social media can pose, as well as annual operations security training that covers the broader issue of safeguarding information."

Chief Warrant Officer Barry Lane, a US Coast Guard spokesman, said in an e-mail on Friday, "TikTok is not an application currently used on any official Coast Guard device."

He said Coast Guard members go through security and cyber-awareness training every year.

"This training includes best practices to safeguard sensitive and personal information on social media platforms," he said.

The US Navy did not immediately respond to requests for comment.