KUALA LUMPUR - MALAYSIAN police on Wednesday began investigating the wife of opposition leader Anwar Ibrahim and other top party leaders over a banned gathering to mark his return to active politics.

Wan Azizah Wan Ismail, Mr Anwar's wife, who heads the Keadilan party, was among four people questioned following a rally on Monday which police said was illegal.

'We have answered all their questions and we leave it to the police,' Ms Azizah later told reporters.

'If you compare what happened here to (the way the police treat the ruling United Malays National Organisation), it would seem that we are getting more attention,' she said in a reference to the way police disrupted Monday's gathering.

Mr Anwar, a former deputy prime minister who was sacked and jailed a decade ago, said at the rally he had enough support to form a government but would not act until he had a more comfortable majority.

But police halted his speech midway and closed down the rally, which drew 10,000 supporters to celebrate the end of his ban from politics.

Party vice president Azmin Ali, Selangor state chief minister Khalid Ibrahim and his aide were also ordered to turn up at police headquarters.

Mr Azmin said he did not understand why police were keen to investigate gathering.

'(The police) had a series of meetings (with organisers) prior to the event. Even on the day itself, they sent down senior police officers to discuss the traffic flow outside the club,' he added.

The rally marked the expiry of Mr Anwar's official ban from public office.

Once seen as the heir apparent to long-time leader Mahathir Mohamad, he was subsequently convicted on sex and corruption charges and spent six years in jail, before storming back to prominence in March elections.

With Mr Anwar at the helm a reinvigorated opposition seized a third of parliamentary seats and five states in the worst ever showing for the Barisan Nasional coalition that has ruled for half a century.