Kuala Lumpur, Dec 11: Malaysia briefly detained de facto opposition leader Anwar Ibrahim on Tuesday and arrested about a dozen other opposition leaders amid the state's biggest crackdown on anti-government activists in a decade. Immigration officials detained Anwar at the country's main airport on his return from Istanbul via Singapore before clearing him for entry, the former deputy premier told Reuters.

"It's just a clear harassment," Anwar said. "It's a desperate attempt to harass and intimidate the public and deflect the attention from major issues of corruption among UMNO leaders and the judiciary," he added, referring to the main ruling party, the United Malays National Organisation (UMNO). The government denies opposition allegations it is cracking down on legitimate dissent, arguing that police are trying to protect public safety by breaking up street demonstrations and arresting their organisers, including opposition politicians. For the first time since Anwar led mass protests in 1998, hundreds of riot police have turned out onto the streets of the capital in recent weeks, using tear gas and water cannon on anti-government rallies of up to 10,000 people or more.

Police have been manning road blocks around Kuala Lumpur, on and off, for weeks to prevent would-be protesters from converging on the city. On Tuesday, they threw a cordon around Parliament House to prevent a rally demanding free and fair elections.

"It is completely unnecessary, uncalled for and unwarranted. This is not a private club, this is a public place," another opposition leader, Lim Kit Siang, told reporters at parliament, which had been ringed by riot police. Police arrested about a dozen opposition leaders who took part in Tuesday's rally, including a senior official of Anwar's Keadilan (Justice) party, Tian Chua, after the car he was in drove through the police cordon and headed toward parliament.

Tian Chua had planned to hand a memorandum to the Speaker of the Lower House, opposing government plans to amend the constitution to enable the current Election Commission chief to serve another year before his retirement.

A group formed to campaign for electoral reform, Bersih, which staged a protest of around 10,000 people early last month, wants the long-standing commission chief to be replaced before the next election, widely expected to be held early next year.

Prime Minister Abdullah Ahmad Badawi, who came to office in late 2003 promising a crackdown on corruption and greater openness, has rejected criticism that he has allowed his reform agenda to fail and that he is increasingly intolerant of dissent.

On Monday, after police halted an annual human rights march in the capital, he said it was his duty to ensure stability, even if this meant invoking the country's Internal Security Act (ISA), which allows indefinite detention without trial. If I have to sign a detention order, if someone has to be taken in under the ISA ... I'll do it without feeling guilty, without feeling sad. I know that I'm doing my duty," he said.

The government has not yet invoked the ISA during the current street protests. Police have instead charged protesters in court under laws against public assembly then released most on bail.

But one protest group, a small Hindu rights outfit, has angered the government more than any other, for staging a rally of more than 10,000 ethnic Indians in Kuala Lumpur last month.

The Hindu Rights Action Force, which says minority ethnic Indians are being marginalised by the government, is being investigated for alleged terrorist links. One of its supporters, human rights lawyer P. Uthayakumar, was arrested on Tuesday.

Uthayakumar, 46, would be charged later on Tuesday for sedition for statements he made in a book, his aide said.

Police said they had arrested 12 people, including Keadilan Secretary-General Khalid Ibrahim, at the parliament rally. Police had a court order to prevent anyone from gathering outside parliament