(Adds updated advocate general statement, party reaction)

DUBAI, June 16 (Reuters) - Bahrain sentenced opposition leader Sheikh Ali Salman to four years in jail on Tuesday on charges of inciting unrest, a decision that an opposition group said could stoke more protests in the Sunni Muslim-ruled kingdom.

Salman is the senior figure in Shi'ite opposition to be jailed since anti-government protests erupted in 2011, at the height of the region's "Arab Spring" uprisings.

"The Higher Criminal Court sentenced the secretary general of one of Bahrain's political societies to four years imprisonment," advocate general Haroon Al-Zayani was quoted as telling state news agency BNA.

Salman, who was not named in the statement, was convicted on charges of "publicly inciting hatred, an act which disturbed public peace, inciting non-compliance with the law and insulting public institutions."

Bahrain, which hosts the U.S. Fifth Fleet, has experienced sporadic turmoil since mass protests in 2011 led by majority Shi'ites demanding reforms and a bigger role in government. That uprising was put down with military help from Saudi Arabia.

The al Wefaq Islamic Society headed by Salman, a 49-year old Shi'ite cleric, confirmed he had been sentenced. It condemned the ruling and vowed to keep up pressure on the authorities.

"The sentence gives a new lease on life to the crisis and gives greater legitimacy to mobilize. The people have no choice but to continue in their peaceful popular movement," it said in a statement on its official website. "People will not return to their homes and will not relent in their demands."

Salman was acquitted of the most serious charge, promoting the overthrow of the political system by force, the advocate general said in its statement. He has denied the charges and has dismissed the trial as bid to muzzle dissent.

Amnesty International called on Bahrain on Monday to free Salman, calling him a "prisoner of conscience" and saying his trial was unfair.

The island kingdom says it has made significant political reforms and increased oversight of security forces. Opponents say abuses continue.

With a political accord between the government and opposition remaining elusive, deadly bomb attacks on Bahraini security forces have increased.

In a statement on Monday, the government said the "serious charges" against Salman were rightly regarded as a criminal offence, and that he had received a fair trial.

"Ali Salman's case relates to criminal charges, specifically incitement of hatred, as well as inciting violence. The charges and subsequent trial are wholly unrelated to any political views he may hold," the government statement said.

(Reporting By Noah Browning; Editing by Larry King) ((noah.browning@thomsonreuters.com;))

Keywords: BAHRAIN TRIAL/