One of the leaders of the opposition coalition Southern Movement, he had reportedly called for a “Day of Rage” against the Yemeni government to be held in the south.
“If Hassan Ba’oom is being held solely for peacefully exercising his right to freedom of expression and assembly, he is a prisoner of conscience and must be released immediately and unconditionally,” said Luther.
“The authorities must also ensure he receives all necessary medical treatment without delay and that he is protected from torture and other ill-treatment.”
Scores of others have been arrested following protests in Aden on February 16. They are believed to be held without charge or trial in al-Mansurah Central Prison.
Protests have been taking place in Aden and other places in southern Yemen since 2007 against perceived discrimination by the government against southerners and, increasingly, in favour of the secession of the south of the country.
Following demonstrations in the capital Sana’a and other cities in recent weeks calling for the president to stand down and regime change, protesters in Aden have started to make similar demands.
The Southern Movement is an umbrella movement of political groups, some of which want the south of the country to secede.