Kuala Lumpur: Malaysia on Tuesday detained opposition leader Anwar Ibrahim and a dozen opposition leaders, amid growing complaints of government harassment.

Police also arrested human rights lawyer P. Uthayakumar, who helped organise 10,000 ethnic Indians to protest last month against racial discrimination.

Uthayakumar would be charged later on Tuesday for sedition for statements he made in a book, his aide said without elaborating.

Meanwhile, Immigration officials detained Ibrahim at the country's main airport upon returning from Istanbul via Singapore before being cleared for entry.

"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."

UMNO is the United Malays National Organisation, Malaysia's main ruling party.

In the incident that lasted about half an hour, Anwar said he was stopped because his name was on immigration's "suspects list" although he was not informed why.

Anwar said he was allowed to leave after a senior immigration officer came out to speak to him, but his name remains on the list, which could bar him from leaving Malaysia.

In the Malaysian capital on Tuesday, dozens of policemen blocked the main entrance to the parliament building to foil an opposition-led rally demanding free and fair elections.

Police arrested about a dozen opposition leaders, including the leader of Anwar's Keadilan (Justice) party, Tian Chua, after the car he was travelling in broke through a police cordon and headed toward parliament .