London (CNN) -- Rights groups have slammed a lunch hosted by Britain's Queen Elizabeth II on Friday for including monarchs criticized for their countries' human rights records. Among those who attended the event at Windsor Castle is the king of Bahrain, whose government has come under fire for its crackdown on anti-government protests last year and its handling of continuing unrest. Swaziland's King Mswati III, accused by critics of enjoying a lavish lifestyle at public expense while his people suffer great poverty, was also there. The monarchs' lunch, with a menu that included English asparagus, lamb from Windsor and strawberries from Kent, is part of celebrations of the Queen's Diamond Jubilee, marking her 60 years on the throne. It will be followed by an evening banquet at Buckingham Palace hosted by Prince Charles and the Duchess of Cornwall.
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NEW: The kings of Bahrain and Swaziland are among the royals to attend the Jubilee lunch
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NEW: Queen Elizabeth II greets each monarch on their arrival at Windsor Castle
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Campaigners say monarchs from countries with poor human rights records should not be invited
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Foreign Office says UK's relationship with Bahrain means it can push for more reforms
He called for the invitations to monarchs heading nations with poor records on rights to be withdrawn immediately and said protesters would stage a rally outside @placeholder as royals arrive for the dinner.
Bahrain's king is not on the guest list for the smaller evening event, but @placeholder's monarch is among those invited to both lunch and dinner.