Short-form social video app TikTok came under sharp scrutiny in a Senate subcommittee hearing Tuesday following the U.S. government launching a national security review of the fast-growing social media platform's Chinese-based parent company last week.

"If you don't know what TikTok is, you should," Sen. Josh Hawley, R-Mo., said at the onset of the hearing he chaired, calling it "a Chinese-owned social media platform so popular among teens that Mark Zuckerberg is reportedly spooked."

"For Facebook, the fear is lost social media market share. For the rest of us, the fear is somewhat different," he continued. "A company compromised by the Chinese Communist Party knows where your children are, knows what they look like, what their voices sound like, what they're watching, and what they share with each other."

The company was invited, along with Apple, to appear in the Senate Judiciary Subcommittee on Crime and Terrorism hearing titled "How Corporations and Big Tech Leave Our Data Exposed to Criminals, China, and Other Bad Actors." Both companies declined to appear.

In a letter to the subcommittee obtained by NBC News, TikTok U.S. general manager Vanessa Pappas said the company, owned by Chinese-based ByteDance, does not store any U.S. user data in China and does not remove content from its platform at the Chinese government's behest. Pappas also said the company pledges to engage in ongoing, independent audits of its data security practices, adding that TikTok has "a dedicated technical team focused on adhering to robust cybersecurity policies, data privacy and security practices."

"No governments, foreign or domestic, direct how we moderate TikTok content — that is left in the capable hands of professional content moderation teams led by our U.S.-based team," she wrote, adding, "TikTok does not remove content based on sensitivities related to China (or other countries). We never been asked by the Chinese government to remove any content, and we would not do so if asked."

That answer did not ease Hawley's qualms, and experts present at the hearing pointed to Chinese laws that compel organizations based in the country to comply with "state intelligence work."

"TikTok claims they don't store American user data in China," said Hawley, who has positioned himself as one of Congress' most vehement critics of major tech platforms. "That's nice, but all it takes is one knock on the door of their parent company based in China from a Communist Party official for that data to be transferred to the Chinese government's hands whenever they need it."

TikTok "should have been here today, but after this letter to this committee, they must now appear, under oath, to tell the truth about their company and its ambitions and what they're doing with our data," Hawley added. "The threat isn't just to children's privacy, it's a threat to our national security."

One of the fastest growing social media platforms globally, TikTok has been the subject of growing scrutiny from lawmakers and regulators. Late last week, the Committee on Foreign Investment in the United States (CFIUS), which reviews deals by foreign businesses for possible national security risks, launched an inquiry into ByteDance's $1 billion acquisition of the social media app Musical.ly in 2017, two people familiar with the matter told Reuters. Musical.ly later became TikTok.

The review came after lawmakers questioned whether China was working to censor content on the platform or compromise any user data.

TikTok has become one of the most popular social media platforms for teenagers and young adults, with about 60 percent of its more than 26 million monthly active users being between the ages of 16 and 24, the company said earlier this year.

"While we cannot comment on ongoing regulatory processes, TikTok has made clear that we have no higher priority than earning the trust of users and regulators in the US," a TikTok spokesperson said in a statement. "Part of that effort includes working with Congress and we are committed to doing so."

A Treasury Department spokesman said the department "does not comment on information relating to specific CFIUS cases, including whether or not certain parties have filed notices for review."