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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 said on Sunday.

The New York-based rights group urged EU foreign policy chief Catherine Ashton and other European officials who were meeting with Gulf counterparts, including Saudi Arabia, in Manama on Sunday to condemn the convictions.

Eastern Province has seen occasional protests by minority Shi'ite Muslims over the past two years against alleged discrimination and negligence, which the Riyadh government denies.

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"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," Joe Stork, Human Rights Watch's deputy Middle East director, said in a statement.

"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 Shi'ite from 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, speaking on condition of anonymity.

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, Human Rights Watch 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 Shi'ites over the deployment of Saudi forces to nearby Bahrain to help crush anti-government demonstrations there. A majority of Bahraini citizens are Shi'ites.

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 Shi'ites 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.