Abdulhadi al-Khawaja, who is a Danish citizen and has been refusing food since Feb. 8, is serving a life sentence for his role in last year's uprising by the island nation's Shiite majority against a Western-backed Sunni monarchy.
The Bahrain News Agency said the Supreme Judicial Council has declined to hand him over to Danish authorities because the law prevents transfers of "accused and convicted persons to foreign countries."
Bahrain's opposition supporters have been staging daily rallies for al-Khawaja's release, frequently clashing with security forces. The demonstrations have helped fuel rising tensions in the kingdom just two weeks before it is to stage the Formula One grand prix race—its premier international event that was canceled last year because of the political unrest.
The government said last week that al-Khawaja has lost 10 kilograms (22 pounds), while his lawyer said that al-Khawaja is weak but was conscious on Friday when he visited him in the hospital.
Al-Khawaja's declining health has prompted appeals from groups such as Amnesty International, which last week urged Bahrain to free him because of fears he could die. The Danish government said last week it has been "exerting maximum efforts" to have al-Khawaja sent to Denmark for medical treatment.
There was no immediate comment from Danish authorities on Bahrain's decision Sunday.
Al-Khawaja, 52, is a former Middle East and North Africa director of the Ireland-based Frontline Defenders Rights organization. He has also documented human rights abuses in Bahrain for international rights groups such as Amnesty International and Human Rights Watch.
Having lived in exile in Denmark for decades, he returned to Bahrain after the government announced a general amnesty in 2001.
He was arrested last April during a government crackdown on dissent. Al-Khawaja is one of seven opposition figures who were sentenced to life imprisonment in a special security court, which was set up after Bahrain imposed martial law last March to quell political unrest in the tiny, but strategically important nation.
Hundreds of other Bahrainis, including protesters, activists, athletes and Shiite professionals such as doctors and nurses, have been tried in the court. Dozens were jailed after being convicted of anti-state crimes, including medics who treated injured protesters during the unrest.
Bahrain lifted martial law in June. The special tribunal was disbanded in November and all protest-related trials were transferred to civilian courts. Al-Khawaja's lawyers appealed his conviction in Bahrain's highest court on Monday when judges refused to release him on bail.
At least 50 people have died during the 14-months revolt in Bahrain, which is the home of the U.S. Navy's 5th Fleet.