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.

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