Bahrain's King Hamad on Monday pardoned leading rights activist Nabeel Rajab, serving a six-month jail sentence, for "health reasons", the official news agency BNA reported.

It said the king issued a decree granting the activist "a special pardon for health reasons", but without elaborating.

In May, an appeals court upheld a six-month prison sentence for Rajab, a member of Bahrain's Shiite majority arrested in April, for insulting public institutions on Twitter.