For months, Instagram has watched and waited to see what would happen to rival TikTok under a new federal law that would ban the app in the United States. On Sunday, the day that law took effect, Instagram pounced.

The social media app, which is owned by Meta, announced a new app called Edits, a video-editing product that appeared to be a clone of CapCut, which is used by millions of people to stitch together short videos for TikTok. CapCut and TikTok are owned by ByteDance, the Chinese internet giant, which led to U.S. scrutiny of the apps for national security reasons.

“There’s a lot going on in the world right now,” Adam Mosseri, head of Instagram, said in a post to the platform on Sunday. “No matter what happens, we think it’s our job to make the most compelling creative tools for those of you who create videos.”

TikTok and its sister apps, CapCut and Lemon8, have long given U.S. social media apps a run for their money. TikTok has 170 million U.S. users and it had said in legal filings that it could not afford to go dark even temporarily because it would suffer a competitive disadvantage in one of its biggest markets.

Late Saturday, hours before the federal law banning TikTok was set to take effect, TikTok, CapCut and Lemon8 became unavailable, though TikTok flickered back to life on Sunday as President-elect Donald J. Trump said he planned to issue an executive order this week to stall the ban.

TikTok’s competitors have not waited to make hay from the situation. Mr. Mosseri described Edits as designed specifically for creators to edit video on their phones and to save ideas for other videos that they might want to post later.

Mr. Mosseri said creators could use Edits to work on videos and post them to any platform they wanted, not just Instagram. Influencers often used CapCut to work on videos and post them to multiple platforms, including TikTok, Instagram and YouTube.

Mr. Mosseri said people could preorder Edits in the Apple App Store starting Sunday and that the app would be available for Android in February.

Mark Zuckerberg, Meta’s chief executive, has talked publicly about watching TikTok’s dilemma play out. His Silicon Valley company has hired lobbyists to make the case that American tech firms must come first, as part of winning a tech race against China.

At a meeting with employees last week, Meta’s chief marketing officer also said the company needed to prepare for a potential migration of TikTok’s users to Meta’s apps and should devote staff and other resources to those possible developments. Instagram also changed its layout for some users last week, formatting content in a vertical, rectangular shape reminiscent of TikTok.

Instagram has long angled to mimic TikTok’s success. In 2020, Instagram launched Reels, an almost exact clone of TikTok’s marquee short-form video format. Reels has grown to be one of the most popular features on Instagram and Facebook.

U.S. internet users have said they would most likely watch Instagram Reels if TikTok was banned, according to a recent survey from TD Cowen of 2,500 consumers. Reels would attract 29 percent of respondents, while 23 percent said they would spend more time on YouTube Shorts, and 15 percent would look for a new app, according to the survey.

Among advertisers, Instagram’s advantage appeared even starker, with 56 percent of ad buyers telling TD Cowen in a survey last quarter that their clients most wanted to advertise on Reels this year. Another 24 percent favored YouTube Shorts, while 20 percent preferred TikTok.

Madison Malone Kircher contributed reporting from New York.