Facebook is banning private sales of guns on its flagship social network and its Instagram photo-sharing service, a move designed to clamp down on unlicensed gun transactions.

Facebook already prohibits people from offering marijuana, pharmaceuticals and illegal drugs for sale, and the company said Friday it was updating its policy to include guns. The ban applies to private, person-to-person sales of guns. Licensed gun dealers and gun clubs can still maintain Facebook pages and post on Instagram.

Although Facebook was not directly involved in gun sales, it has served as a forum for gun sales to be negotiated, without people having to undergo background checks. The social network, with 1.6 billion monthly visitors, had become one of the world’s largest marketplaces for guns and was increasingly evolving into an e-commerce site where it could facilitate transactions of goods.

In January, President Barack Obama gave a speech promising to tighten enforcement of laws governing unlicensed gun sales. In response, some individual sellers said they would turn to sites like Facebook, which allowed them to freely advertise guns for sale.

Facebook said it would rely on its vast network of users to report any violations of the new rules, and would remove any post that violated the policy. Beyond that, the company said it could ban users or severely limit the ways they post on Facebook.