Saudi Arabia has sentenced seven activists from its restive Eastern Province to prison terms ranging from five to 10 years for posting messages on Facebook calling for anti-government protests, Human Rights Watch (HRW) said.
Minority Shia Muslims have held protests in Eastern Province over the past two years against alleged discrimination and negligence, which the Riyadh government denies.
"Sending people off to years in prison for peaceful Facebook posts sends a strong message that there's no safe way to speak out in Saudi Arabia, even on online social networks," said Joe Stork, HRW's deputy Middle East director.
The New York-based rights group urged EU foreign policy chief Catherine Ashton and other European officials to condemn the convictions. Ashton was due to meet Gulf counterparts, including from Saudi Arabia, in Manama, Bahrain on Sunday.
"If the EU doesn't raise these cases with Saudi officials this weekend, its silence will look like craven compliance with the rights abuses of an authoritarian state."
Saudi Interior Ministry officials were not immediately available for comment.
A Saudi-based human rights campaigner said the activists were all Shia from Eastern Province's al-Ahsa governorate, who had set up Facebook pages to urge people to stage demonstrations.
"The sectarian situation in the region made the sentences tough and unreasonable," he said.
Human Rights Watch said the seven men were detained in September 2011 and had spent a year and a half in prison before being tried by a special tribunal set up in 2008 to handle terrorism-related cases.
The court did not charge the men with directly participating in the protests, HRW said, rather with inciting "protests, illegal gathering, and breaking allegiance with the king".
Saudi Arabia swiftly moved in early 2011 to quell protests by minority Shia over the deployment of Saudi forces to nearby Bahrain to help crush anti-government demonstrations there.
A majority of Bahraini citizens are Shia.
But discontent lingers on with occasional protests in eastern Saudi Arabia, where at least 20 people have been killed by security forces since 2011.
On Thursday, thousands of Shia protested against the kingdom's ruling al-Saud family at the funeral of a wanted man shot dead by police, an incident that ended months of relative calm in the province.