The BBC's Frances Harrison: "Garlanded with flowers, Mr Lim addressed his supporters"

Lim Guan Eng, the leader of the youth wing of the Democratic Action Party, was serving two concurrent 18-month sentences, but was released on good behaviour.

His political allies hope his release will galvanise a disparate opposition in forthcoming elections.

National symbols

Mr Lim was released from Kajang prison outside the capital Kuala Lumpur shortly after daybreak.

Several hundred activists from Malaysia's four main opposition parties gathered outside the prison, waving flags, party banners and balloons, and shouting "reformasi" (reform), the slogan of the jailed former Finance Minister Anwar Ibrahim.

Lim and Anwar have become national symbols of the growing opposition to Prime Minister Mahathir Mohamad's 18-year rule.

Frances Harrison reports on the background to Lim Guan Eng's imprisonment

Lim Guan Eng was convicted in 1997 for publishing in 1995 a pamphlet, entitled "Ceramah Kisah Benar" (The True Story), which criticised the government's handling of allegations of statutory rape against a senior politician who was never prosecuted.

The politician denies any relationship with the girl.

Mr Lim's conviction was condemned by rights groups and opposition leaders.

Although Mr Lim is now free, he is barred from running for public office for five years from his release.

London-based Amnesty International called the charges against him "politically motivated, designed to intimidate dissenting voices".

The four main opposition parties, divided by ideology, see Mr Lim and Mr Anwar as unifying symbols in general elections which must be held by June next year but are expected before the end of this year.

Leaders of the four main opposition parties - DAP, Parti Keadilan Nasional (National Justice Party) led by Mr Anwar's wife Wan Azizah Wan Ismail, the Islamic fundamentalist Parti Islam se-Malaysia (PAS) and Parti Rakyat Malaysia - are planning a joint rally later on Wednesday, with Lim Guan Eng as the main speaker.