WASHINGTON (Reuters) - President-elect Donald Trump would not rule out continued Chinese ownership of TikTok if steps were taken to ensure that American users' data was protected and stored in the U.S., incoming National Security Adviser Mike Waltz told CNN on Sunday.

TikTok stopped working for its 170 American users on Sunday after a law took effect banning the app's continued operation over concerns that Americans' data could be misused by Chinese officials.

Waltz, a member of Congress whose appointment as security adviser would be subject to Senate confirmation, told CNN the president-elect is working to "save TikTok" and doesn't rule out continued Chinese ownership coupled with "firewalls to make sure that the data is protected here on U.S. soil."

Trump has said he would "most likely" give TikTok a 90-day reprieve from a ban after he takes office on Monday, a promise TikTok cited in a notice posted to users on the app.

Waltz also spoke to CBS News on Sunday and said Trump needed time to sort out issues related to TikTok while adding that an extension was needed for TikTok to evaluate proposed buyers.

However, Republican House of Representatives Speaker Mike Johnson sent contradictory signals, saying that he believed Trump would push for TikTok parent ByteDance to sell the app.

"The way we read that is that he's going to try to force along a true divestiture, changing of hands, the ownership," Johnson said. "It's not the platform that members of Congress were concerned about. It's the Chinese Communist Party"

Some of Trump's fellow Republicans in Congress have opposed the idea of the extension for TikTok.

Republican U.S. Senators Tom Cotton, who chairs the Senate Select Committee on Intelligence, and Pete Ricketts said in a joint statement on Sunday that "there's no legal basis for any kind of 'extension' of its (ban's) effective date."