Saudi Arabia has "temporarily" released eight activists arrested last month for protesting against the country's ban on women driving.

The five women and three men were arrested for allegedly undermining "the security and stability of the Kingdom, its social peace and national unity," Saudi Arabia Public Prosecution said in a statement on Saturday.

But nine other women's rights activists remain in custody due to confessions and "sufficient evidence against them," the statement said.

Saudi authorities claim those activists admitted to communicating and cooperating with "individuals and organizations hostile" to the Kingdom; recruiting people in a position to obtain confidential information and official documents to harm the country's interests; and providing financial and moral support to hostile elements abroad.

The detainees were not identified.

The State Security Presidency, a powerful security apparatus that reports directly to the King and 32-year-old crown prince, had been monitoring the detainees prior to their arrest, according to Saudi Arabia's official news agency.

Women will be able to drive June 24

The activists were arrested weeks before Saudi Arabia is set to lift a ban on women's driving June 24. Many of the activists have been identified by local media and rights groups as leading women's rights activists.

While the planned change has been heralded around the world, the arrests just weeks ago concerned women's rights activists and those monitoring the social reform agenda of Crown Prince Mohammad bin Salman bin Abdulaziz Al Saud.

"We are back to square one," Sydney-based Saudi activist and author Manal Al-Sharif had told CNN.

"We used to live in a police state; if you speak up you go to jail. And then there would be a defamation campaign against you, saying all sort of untrue things. Character assassination."

Those familiar with the detained activists say they wanted more reforms. They say the activists feared changes would stop if they did not continue to work for greater rights.

One of the most high-profile activists arrested in recent months, Loujain Al-Hathloul, was previously detained for 73 days in 2014 after trying to drive from the United Arab Emirates to Saudi Arabia.

Another detained activist, Aziza al-Yousef, 70, is one of the country's earliest activists for the right to drive and signed a petition in recent years calling for an end to guardianship laws.