The UK advertising watchdog has ruled against online games Moshi Monsters and Bin Weevils in a crackdown on adverts pressuring children to spend money.

The Advertising Standards Authority (ASA) said both "directly pressured" young players to pay subscriptions.

It said Moshi Monsters told children that members would be "super popular", while Bin Weevils' options to pay subscriptions were phrased as commands.

The publishers said they were cooperating with the ASA.

"Although it was possible to play the games without spending real money or sharing the game, certain activities required participation in a paid-membership system, which entitled members to additional benefits," the ASA said.

"Both games contained language and prominent calls to action that put pressure on young players to purchase a subscription to take part in additional gameplay. We considered that text, including "Become a Member", "JOIN NOW", directly exhorted children to purchase membership subscriptions as well as in-game 'currency'."

It said that phrases used in Moshi Monsters - such as "The Super Moshis need YOU" - put pressure on children. In Bin Weevils' case, it said that it used imperative phrases, such as "DOSH Top Up" that could be read by children as orders to pay.

It said that putting such pressure on children was prohibited by its advertising code and ordered that the ads should not appear again in those forms.

The ASA added that it would remind publishers to take care with in-game purchase mechanisms aimed at children.

Mind Candy, which publishes Moshi Monsters, said it took its "responsibilities very seriously with regards to how we communicate with all of our fans, especially children".

In a statement, it said: "We have been working with the ASA to ensure that we adhere to best practice and have made changes to the Moshi Monsters game accordingly. We will continue to work with the ASA in any way possible."

The Bin Weevils publisher, 55pixels, said: "As soon as [we] were made aware of the complaint made to the ASA about a potential breach, and once we had understood the area for concern, we changed all our membership pages to comply with their recommendations.

"They subsequently upheld the complaint about the original wording but referenced that we now complied, in the text of the ruling."