(CNN) -- A Bahrain appeals court has upheld all verdicts against 13 defendants accused of plotting to overthrow the regime and breaching the constitution, authorities said Tuesday.
Seven of the sentences upheld are for life in prison, and one of the people sentenced is Abdulhadi al-Khawajah, a prominent activist who ended a 110-day hunger strike earlier this year.
The court reduced the sentence of a 14th defendant to five years and convicted six others, Bahrain's Information Affairs Authority said.
The defendants were arrested for their roles in anti-government demonstrations last year as the Arab Spring movement swept across the region.
Demonstrations in Bahrain failed to gain the traction of other Arab Spring uprisings after a crackdown by authorities in the island state, backed by troops from nearby Saudi Arabia and the United Arab Emirates.
Last November, Bahrain's Independent Commission of Inquiry issued a report critical of authorities' reactions to the protests, which began in February 2011, spurred by uprisings in Tunisia and Egypt.
Bahrain plays a key strategic role in the Middle East and is home to the U.S. Navy's Fifth Fleet headquarters.
Amnesty International called the move "outrageous."
"Today's court decision is another blow to justice and it shows once more that the Bahraini authorities are not on the path of reform but seem rather driven by vindictiveness," said Hassiba Hadj Sahraoui, deputy director of Amnesty International's Middle East and North Africa Program.
"Today's verdict further engulfs Bahrain in injustice. Instead of upholding the sentences, ranging from five years to life in prison, the Bahraini authorities must quash the convictions for the 13 men who are imprisoned solely for peacefully exercising their human rights and release them immediately and unconditionally."
The government defended the court's procedures and decisions, saying it "provided all assurances of a fair trial." It noted that Amnesty International was one of the international entities that attended the trial.
It said the defendants may appeal their sentences to the Supreme Court.
Defendants on the stand were allowed "to sit by their lawyers' sides without any restriction on their freedoms and they were given the opportunity to speak in their own defense," the government said.
"Attorneys were allowed full access to meet with the defendants before and after the trials," the government said. "The court provided all their health requirements upon their request and at all times.
Amnesty International urged a probe into defendants' allegations of torture and mistreatment, including sexual assault in detention to coerce confessions.
But the government said the "defendants received full medical care during their incarceration."