Jeddah: Dozens of Saudis have signed up to join a two-day hunger strike this week to protest against the detention of a prominent rights activist, a rights group said.

Mohammad Al Bajadi was detained in March 2011, activists said, for supporting families demonstrating outside the Interior Ministry in Riyadh to demand the release of detained relatives. His trial, on charges including tarnishing the reputation of the state, has been suspended as he refused to recognise the court.

The Saudi Civil and Political Rights Association (ACPRA), which is promoting the hunger strike on Thursday and Friday, said 38 activists had signed up on its website so far to participate in the action.

"This weekend we will meet in a public place and strike in public, in a farmhouse in Riyadh, the Qurtuba district," activist Mohammad Al Qah'tani told Reuters on Monday.

"We hope to shed light on Mohammad Al Bajadi's case and others like him because unfortunately the state does not listen to the people, so we want to alert the international community to put pressure" on it, he said.

An Interior Ministry spokesman said he was not aware of the case and declined to make any further comment.

Independent rights groups estimate that the number of prisoners ranges between 12,000-30,000 but the Interior Ministry denies there are any political prisoners in the kingdom. The ministry said last year it was holding 5,696 people for "militant"-related cases, most of whom appeared before courts.

The government-affiliated Human Rights Commission, which reports directly to King Abdullah, said in a statement on Monday that there are around 4,600 prisoners held in prisons, without giving any further details.