Bahrain's highest court on Monday upheld the sentences of 13 opposition activists convicted of attempting to overthrow the government during 2011 protests.
The court's decision cannot be appealed, the al-Watan newspaper reported.
The main opposition group, Al-Wefaq, said the sentence was political and reflected the judiciary's lack of independence since "it has been used and controlled by the regime in the political conflict to punish dissidents."
"The final verdict ... reveals that the regime has no desire to review (it)," the group said. "There seems to be no Bahraini solution for the crisis due to the lack of a serious will to resolve it."
Amnesty International said the verdict is "further proof of how the country's justice system simply cannot be relied on."
“This unjust decision will confirm the view of many that the judiciary is more concerned about toeing the government's line than upholding the rule of law and the rights of all Bahrainis," said Hassiba Hadj Sahraoui, Amnesty International"s Deputy Director for the Middle East and North Africa.
"In order to maintain any credibility at all the Bahraini authorities must release these 13 people who have been imprisoned simply for exercising their rights to freedom of expression and assembly," she added.
Protests in which Bahrain's Shiite majority have demanded political reform and greater freedoms began on February 14, 2011.
In May, King Hamad bin Isa Al Khalifa introduced constitutional reforms which he said will strengthen the parliament and limit the powers of the royal family.
Despite the government hopes, protests continued as the opposition denounced the reforms as inadequate.
The 13 were among 20 opposition leaders and activists who were originally convicted - with sentences ranging from five years to life - by a special military tribunal for their involvement in predominantly Shiite protests against the ruling Sunni royal family.
A commission appointed by the government had recommended a retrial in a civil court, saying it had found evidence of confessions obtained through torture and that the activists had not been allowed adequate access to their lawyers.
All 20, seven of whom were tried in absentia, lost the appeal in a civilian court in September. Only 13 filed appeals to Bahrain's highest court.
Seven of the defendants were sentenced to life in prison. Among them was Abdulhadi al-Khawaja who holds Bahraini and Danish citizenship.
Denmark's Foreign Minister Villy Sovndal said the sentences "were very disappointing."
"It is important to remember that this is a Danish national who has been sentenced in connection with his struggle for human rights and who has been subjected to torture," Sovndal said.
"We will, along with countries and international organizations that support the Danish stance, including the European Union and the United Nations, discuss what possibilities can lead to the release of al-Khawaja and the other human rights and democracy activists in Bahrain," he added.
Al-Khawaja and his family had spent 12 years in exile before returning to the Gulf island in 1999, just as Bahrain's then new ruler, Sheikh Hamad bin Isa al-Khalifa, vowed reforms as he rose to power and sought to quell unrest that began in the mid 1990s.
This was the second time al-Khawaja was accused of attempting to overthrow the regime. He was detained in February 2007, but was released within hours after clashes broke out between his supporters and police.
The trial drew a wave of international criticism and raised tensions on the small strategic Gulf island that serves as home to a US naval command.
Human rights groups and Bahrain's Western allies have repeatedly called for the activists' release.