Altria shares slid Tuesday as the tobacco company warned that cigarette sales declines are accelerating and it's "too soon" to judge Juul's international expansion, a key piece of Altria's nearly $13 billion bet on the e-cigarette giant.

Cigarette sales have been declining for years, though they've started falling faster than usual, forcing the maker of Marlboros to search for growth in new products like e-cigarettes, oral nicotine pouches and cannabis.

Altria late last year invested $12.8 billion for a 35% stake in Juul, a start-up that dominated the e-cigarette category within a few years of entering the market but faces intense scrutiny for its popularity among teenagers. Critics have worried from the beginning that Altria paid too much for too little. Those concerns were raised again Tuesday as analysts pressed Altria executives on a call reviewing the company's second-quarter earnings results.

Altria expects cigarette volumes in the U.S. to decline by 5% to 6% this year, which the company attributes to cigarette smokers switching to e-cigarettes. Altria has now revised the estimate twice this year. The company initially forecast volumes to fall by 3.5% to 5%.

Looking ahead, Altria said it expects total domestic cigarette industry volumes to decline to 4% to 6% through 2023, up from the previously forecast range of 4% to 5%. Altria attributed this partly to 18 states hiking the smoking age to 21. Lawmakers are also considering raising the federal tobacco buying age.

Critics of Altria's investment in Juul worry that its success comes at Altria's detriment in the U.S. since people might stop buying Marlboro — the largest cigarette brand in the U.S. — or Altria's other cigarette brands. Altria has pinned its hopes on Juul's growth overseas, though Altria CEO Howard Willard said it's "too soon" to judge the results. Altria has not yet reported Juul's financials in its earnings report because the deal is still undergoing regulatory review.

"There is still a bit of investment spending mode, both domestically and overseas, and I think it's simply too soon to make a judgment on the progress they're making overseas," he said. "That's more of early days there."

Shares of the company fell more than 5% Tuesday before paring back losses. The company's shares closed down 3.6% to $48.50.