* Charges include intent to overthrow government
* Ruling could inflame tension in Gulf Arab state
* U.S. wants to help restore calm in ally
* Case has drawn international criticism
By Rania El Gamal
DUBAI, Jan 7 (Reuters) - Bahrain's highest court upheld prison sentences against 13 leaders of the 2011 uprising on Monday, a defence lawyer said, a ruling that could stir up further unrest in the U.S.-allied Gulf Arab state.
The case has drawn international criticism from rights groups and come under scrutiny from U.S. officials keen for acquittals to help restore calm in a country it counts as a regional ally against Iran.
Bahrain, where the U.S. Fifth Fleet is based, has been in political turmoil since a protest movement led by majority Shi'ite Muslims erupted in February 2011 during a tide of revolts against governments across the Arab world. Bahrain accuses Shi'ite power Iran of encouraging the unrest.
The sentences, originally handed down by a military court in June 2011 and upheld by a civilian court in September last year, range from five years in prison to life sentences.
"This verdict is final, there are no more appeals possible, it is the last stage of litigation," lawyer Mohammed al-Jishi told Reuters by telephone from Manama.
Twenty uprising leaders had been sentenced but only 13 filed appeals. The remaining seven men had been tried in absentia because they were out of the country or in hiding, Jishi said.
Bahrain's main opposition Al Wefaq condemned the decision. "These judgments confirmed the rulings issued before by the military court which were condemned by the whole world. I think it is accurate to call these rulings political persecution," Wefaq leader Sheikh Ali Salman told Reuters.
"It confirms that the Bahrain regime is refusing to take its chances to reform and seems to be deepening its own human rights crisis," said Brian Dooley, director of the Human Rights Defenders Program at U.S.-based group Human Rights First.
The men who received life sentences - 25 years in Bahrain - included rights activist Abdulhadi al-Khawaja and opposition leader Hassan Mushaimaa, who has advocated turning the kingdom of Bahrain into a republic.
Ibrahim Sharif, leader of the opposition Waad party and the only Sunni among those convicted in the case, is serving a five-year sentence.
The hearing was attended by a number of foreign diplomats, Jishi said, highlighting fears that the outcome could have an impact on unrest in the island kingdom.
Several protesters gathered in front of the court on Monday in support of the uprising leaders, Wefaq said via Twitter.
ACCUSED SAY THEY WANTED ONLY DEMOCRATIC REFORM
The Sunni Muslim ruling Al Khalifa family, backed by troops from Saudi Arabia and police from the United Arab Emirates, put down the uprising with martial law. Thousands were arrested and military trials were conducted during the martial law period.
Washington has called on its ally to talk to the opposition, but unrest has continued. Police and demonstrators clash almost daily and each side blames the other for the violence.
The main charges the convicted men faced were "forming a terrorist group with intent to overthrow the system of government", as well as collaboration with a foreign state.
The men deny all charges, saying they wanted only democratic reform in the Gulf Arab monarchy.
In September, a prosecution official said six of the men were guilty of having "intelligence contact" with Iran and its Lebanese Shi'ite militant ally Hezbollah.
The protest leaders are viewed by some Bahrainis as popular heroes whose release could reinvigorate the democracy movement, which demands parliamentary powers to legislate and form governments. Bahraini Shi'ites say they face discrimination, a charge the government denies.