RIYADH - Saudi Arabia arrested prominent rights campaigner Mohammed al-Bajadi, Amnesty International said on Friday, as part of a crackdown mostly targeting advocates of women's rights in the conservative kingdom.Four activists have been released but up to seven others remain in detention. Most are women who previously campaigned for the right to drive and an end to the kingdom’s male guardianship system, which requires women to obtain the consent of a male relative for major decisions.The government announced last week that seven people had been arrested for suspicious contacts with foreign entities and offering financial support to "enemies overseas", and said other suspects were being sought. It did not name them.State-backed media have labeled those held as "agents of embassies", unnerving diplomats in Saudi Arabia, a key US ally which has appealed to the West for massive investments to help transform its economy away from oil.A security spokesman was not immediately available to comment on the latest detention.The arrests come a month before a ban on women driving is set to end, which has been hailed as proof of a new progressive trend under Crown Prince Mohammed bin Salman, but accompanied by a crackdown on dissent.Activists and diplomats have speculated that the detentions may be aimed at appeasing conservative elements opposed to social reforms which include new cinemas, public concerts and an easing of gender segregation. It may also be a message to activists not to push demands out of sync with the government’s own agenda, they said.Bajadi is a founding member of the banned Saudi Civil and Political Rights Association, which has accused the security forces of abuses. He has been detained previously and spent several years in prison.Saudi Arabia, an absolute monarchy, bans most political activity and brooks little public criticism of the government or the Al Saud ruling family."This new arrest is another worrying development in the continued crackdown on human rights defenders in Saudi Arabia," said Samah Hadid, Amnesty's Middle East Director of Campaigns. "We call on the authorities to release all human rights activists immediately."