London (CNN) Britain's royal family has told social media users to show "courtesy, kindness and respect" when interacting with its online posts, after repeated cases of online abuse directed at Duchesses Meghan and Kate.

The family released a set of guidelines for "anyone engaging with our social media channels" on Monday, banning any "obscene, offensive, threatening, abusive, hateful" and discriminatory posts.

Meghan, Duchess of Sussex, and Catherine, Duchess of Cambridge, are frequently the subjects of abusive comments on social media -- something that prompted Kensington Palace to ask social media firms for help in tackling the issue in January.

Much of the abuse is sexist , while racist comments are also made against Meghan, who joined the royal family when she married Prince Harry last year.

The royal family said it reserves the right to delete comments, block users and report posters to police if their contributions do not meet their guidelines, which also state that comments "must not be off-topic, irrelevant or unintelligible."

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