A Bahraini court cut on Tuesday the jail terms against rights activist Nabeel Rajab, who is behind bars for taking part in anti-regime protests, from a total of three years to two, lawyers said.
Amnesty swiftly condemned the ruling as "an insult" while the Shiite opposition in the minority Sunni-ruled Gulf state called for Rajab's immediate release.
The appeals court reduced two jail sentences in cases involving attendance at unauthorised protests from one year to six months each, while it upheld a one-year jail term in a third case, the lawyers said.
It also overturned a sentence against the Shiite activist over a conviction for insulting security forces, for which he had been fined 300 dinars (795 dollars), they said.
Amnesty International said his lawyers would appeal before a higher court to have any jail term scrapped.
The reduction in the jail sentence was "completely hollow given that he shouldn't be serving any time in prison in the first place," said Philip Luther, Amnesty director for the Middle East and North Africa.
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Rajab has "done nothing wrong, except peacefully express his views. A two-year prison sentence, just like a three-year sentence, is an insult and an injustice that can only be rectified by releasing him."
Bahrain's main Shiite opposition group, Al-Wefaq, called for Rajab's immediate release, arguing he had only "exercised his right to demonstrate peacefully".
Rajab, 48, who heads the Bahrain Centre for Human Rights, had led anti-government protests following a crackdown on Shiite-led demonstrations against the Al-Khalifa ruling family in March 2011.
Bahrain continues to witness sporadic protests which have often spiralled into clashes with police.
According to the International Federation for Human Rights, a total of 80 people have been killed in Bahrain since the violence began on February 14, 2011.
The interior ministry says that more than 700 people, including a number of police officers, have been injured in protests.