World leaders including Iran's President Mahmoud Ahmadinejad Thursday opened a forum on Bali with the goal of promoting democracy, but critics are concerned sanctions-hit Tehran will use the talks for its own ends.

A host of heads of state and government have flocked to the Indonesian island amid growing interest in Southeast Asia's biggest economy.

Australian Prime Minister Julia Gillard, Afghan President Hamid Karzai and South Korean President Lee Myung-Bak are among some 1,200 delegates attending the 5th Bali Democracy Forum amid tight security.

Opening the forum, Indonesian Foreign Minister Marty Natalegawa said it allowed countries in the Asia-Pacific region to come together and "engage in an exchange of views on the promotion and strengthening of democratic values and good governance".

But observers say the presence of Ahmadinejad for the first time showed that some regimes were using it to seek legitimacy.

The Iranian leader would use the forum "for his own purposes because he is under pressure by major countries on the nuclear issue," Aleksius Jemadu, from the school of government and global affairs at Pelita Harapan University, told AFP.

"The forum is opening its arms too widely to include everyone," he said, adding that Indonesia should be more selective about who it invited. "To be called a democratic country there are criteria."

Critics said that Ahmadinejad, whose re-election in 2009 was marred by allegations of fraud, would use the forum to combat Iran's growing isolation as sanctions over Tehran's disputed nuclear programme bite.

Attending the summit "fits in perfectly with the Iranian government strategy of building bridges" with countries outside the West, Amnesty International Iran researcher Drewery Dyke told AFP.

Indonesia, a moderate Muslim-majority country, has maintained strong ties with the Islamic republic.

Iran is currently chair of the Non-Aligned Movement, a grouping of 120 countries, and in August hosted a meeting of the group that it trumpeted as a triumph over the West's attempts to isolate it.

The West claims Tehran is seeking to make an atomic bomb, while Iran claims its nuclear drive is for purely peaceful purposes.

Other high-profile participants at the Bali meeting include Thai Prime Minister Yingluck Shinawatra and Turkish Prime Minister Recep Tayyip Erdogan, as well as UN High Commissioner for Human Rights Navi Pillay.

There is tight security for the event, which has in the past attracted few top names, with some 2,300 police officers deployed to guard key areas.

The resort island last month held 10th anniversary commemorations for the October 12, 2002 nightclub bombings that killed 202 people, including 88 Australians.