The former head of the Special Branch of the Malaysian police told the court in central Kuala Lumpur that Mr Anwar's "sexual misbehaviour" had been under investigation as early as 1992.

BBC South East Asia Correspondent Simon Ingram looks forward to the 2nd day of the trial

Mohamed Said Awang testified that police had launched operation "Solid Grip" to look into Mr Anwar's activities before he became deputy prime minister in 1993.

Mr Said said that in 1997 a letter and a sworn statement emerged accusing Mr Anwar of adultery and sodomy.

The prosecution alleges Mr Anwar then persuaded police officers to force retractions by the writers of the two statements.

"A poison-pen letter has become evidence," Mr Anwar said as the trial adjourned after just over three hours.

'Morally unfit'

BBC South East Asia Correspondent Simon Ingram: Defence again attempts to have the case thrown out

The Malaysian Prime Minister, Dr Mahathir Mohamad, sacked Mr Anwar in early September describing him as "morally unfit".

He said he had talked personally to people who said they had sex with Mr Anwar.

Mr Anwar's sacking and subsequent arrest has provoked widespread demonstrations and political unrest.

Anwar says he was beaten after his arrest

But the prosecution told the court it would "prove without any reasonable doubt that the accused used his position of deputy prime minister and finance minister for his own personal interest."

Mr Anwar denies charges of corruption and illicit sex and says he is the victim of a political conspiracy.

Outside the court, armed paramilitary soldiers and riot police again surrounded the courthouse, but no trouble was reported.

Illegal demonstrations

Prime Minister Mahathir said that the illegal demonstrations by Mr Anwar's supporters are "an exercise in futility".

Anwar's family shows its support

Their actions affected the income of petty traders and taxi drivers, and instilled fear in foreigners wanting to visit Malaysia, the Malaysian Bernama newsagency quoted him as saying.

Few seats have been made available in the public gallery for diplomats and human rights observers, and the United States has led international complaints about the exclusion of official observers.

BBC Asia Correspondent Matt Frei: After this trial Malaysia will never be the same again

On Monday Mr Anwar's lawyers had pressed presiding judge Augustine Paul to grant special observer status to several foreign rights groups, including Amnesty International.

"By not allowing the international community to come in and observe the trial, the prime minister is undermining the name of the country," UN Rapporteur and Malaysian lawyer Param Cumaraswamy said outside the court.