A defiant Anwar said the verdict "stinks to high heaven" and vowed to appeal against the judgment that could keep him out of public office until 2008.
"This is an absolute disgrace," the 51-year-old Anwar told the High Court, saying Prime Minister Mahathir Mohamad had subverted the judiciary and the police in a political plot.
Anwar was Mahathir's heir-apparent until last September when tensions between the two reached breaking point and the prime minister fired his deputy.
Outraged Anwar supporters clashed repeatedly with security forces, playing cat and mouse throughout the day in the first anti-government street protests in five months.
Demonstrators threw stones and plastic bottles at riot police, who responded repeatedly with water cannon laced with eye-irritating chemicals and indelible yellow-green dye.
Protesters shouting anti-government slogans lit bonfires in the heart of the capital, throwing rubbish bins, construction planks and newspaper into the flames.
Angry demonstrators broke the windows of a car belonging to private television broadcaster TV3, accused by Anwar's supporters of toeing the government's line.
Police said protesters broke windows in the courthouse and a local police station, injuring a woman constable, as well as windows of several police vehicles.
Riot police hit some protesters on the head and body with batons, leaving several of them bleeding, witnesses said.
Human rights activist Tian Chua, one of the leaders of a new party formed earlier this month by Anwar's wife, and opposition figure Abdul Malek Husin, were detained.
The protests tapered off in the early evening when police rounded up 14 men at a mosque near the courthouse. Police said a total 18 people were arrested.
The protests were among the most intense and widespread in the capital since Anwar's arrest.
Meanwhile, a royal commission recommended that a former police chief be indicted for assaulting Anwar after he was arrested in September, the official Bernama news agency said.
But the maximum jail term it recommended -- three years -- was less than Anwar's six-year conviction.
Anwar was jailed on four corruption counts alleging he directed police in 1997 to obtain retractions from two people who had accused him of sex crimes.
High Court Judge Augustine Paul, explaining his 394-page ruling, said Anwar had abused high political office and deserved stiff punishment even though no money was involved.
"The charges are part of a political conspiracy to destroy me and ensure Datuk Seri Dr Mahathir Mohamad's continued hold on power at whatever cost, even if it means sacrificing whatever little is left of the judiciary's integriy," Anwar said.
Foreign reaction was swift and critical. London-based rights group Amnesty International described Anwar as a prisoner of conscience and called for his immediate release.
"A six-year sentence is an outrage," said former U.S. ambassador to Malaysia John Malott, calling Anwar the world's most famous political prisoner. "The decision was made to get him, and he's been got. It's outrageous."
Anwar could go free in 2003 as prisoners commonly serve two-thirds of their sentence. But the term was heavy enough to disqualify him from parliament or government office for five years from his release.
Written by Reme Ahmad
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