Updated

International rights groups have urged Yemen's Shiite rebels to free a prominent activist who used social media to document the war that has ravaged the impoverished Arab nation.

Human Rights Watch says that Hisham al-Omeisy, a vocal critic of Yemen's warring parties, is being held without charges in an undisclosed location after he was detained on Aug. 14 in the capital, Sanaa.

The New York-based group says al-Omeisy's family and lawyers have had no access to him.

Sarah Leah Whitson, the Mideast director at Human Rights Watch, says Yemen "more than ever needs activists like Hisham al-Omeisy to bring attention to the devastation that war, famine, and disease have wrought on the country and its people."

Amnesty International also made a similar appeal for the release of al-Omeisy on Friday.