WASHINGTON — Senator Mitch McConnell, long one of the tobacco industry’s loyal allies, said on Thursday that he would sponsor legislation to raise the minimum age to 21 for the purchase of tobacco and e-cigarettes.

Mr. McConnell, the Republican Senate majority leader whose home state, Kentucky, is the nation’s second-largest tobacco producer, said he was motivated by the increasing rate of vaping among teenagers and young adults.

Public health agencies have cracked down on e-cigarette companies and distributors in an effort to curb access to the products.

“For some time, I’ve been hearing from the parents who are seeing an unprecedented spike in vaping among their teenage children,” Mr. McConnell said at a news conference Thursday in Louisville, Ky. “In addition, we all know people who started smoking at a young age and who struggled to quit as adults.”