NEW YORK — YouTube, a popular media site for firearms enthusiasts, quietly introduced tighter restrictions this week on videos involving weapons.

YouTube will ban videos that promote or link to websites selling firearms and accessories, including bump stocks, which allow a semiautomatic rifle to fire faster. Additionally, YouTube said it will prohibit videos with instructions on how to assemble firearms. The video site, owned by Alphabet’s Google, has faced intense criticism for hosting videos about guns, bombs, and other deadly weapons.

For many gun-rights supporters, YouTube has been a haven. A current search on the site for ‘‘how to build a gun’’ yields 25 million results.

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