At the massive gathering a spokesman for the Hizb ut-Tahrir's Indonesian branch called for the resurrection of a Muslim caliphate that once reached from North Africa to Asia. He also argued strongly for the implementation of sharia, reports The Brunei Times.

"We are calling (for) the fight against secularism (because it is) the mother of all destruction, and for a stop to all filthy practices such as corruption, the spread of porn through the media," according to Ismail Yusanto, the spokesperson of Hizbut Tahrir Indonesia. "We are also calling on the Muslims to stand up and (be) united to establish shariyah, revive the Khilafah Islamiyyah 'ala Minhajin Nubuwwah (the Islamic caliphate based on the Prophetic tradition) that will bring a blessing for the universe and restore izzul Islam was Muslimin (the dignity of Islam and Muslim.)"

People came from all over the country to attend the event. The British Broadcasting Corp. (BBC) reports that Hizb ut-Tahrir has traditionally excelled at attracting and maintaining a sizable number of followers. The group has a secretive recruiting process and it can take years for prospective members to join, according to the BBC. But a number of supporters attending the event say that, member or not, they believe in the party's overall goals.

Milling around outside the stadium we found 24-year-old Akbar. He was not a member of Hizb ut-Tahrir, but he said: "This conference is not just for one group. In my opinion, if you support there being sharia law in Indonesia, you've got to be here."

Yani, a student from Bogor, said she had come to show there was support for Islam, and support for a Caliphate too. Next to her, Wisnu told us she was there to increase ties with other Muslims. "Maybe I chose Hizb ut-Tahrir because it unites the masses better than other Islamic organisations," she said.

Hizb ut-Tahrir has long been a controversial organization. Some European and Middle Eastern countries have banned the group, which was founded in Jerusalem in 1953, reports The Independent, a British newspaper.

Critics say that its ideology is close to that of violent jihadist groups, and that it radicalises young Muslims who then choose a path of violence. Hizb ut-Tahrir insists that it opposes violence, and it has denounced terrorist bombings in London, Madrid and [the Indonesian island of] Bali. It has a strong presence on university campuses in Britain, some of which have banned it.

Abdullah Gymnastiar, a popular Islamic preacher in Indonesia, said that Hizb ut-Tahrir opposes violence and therefore it would be "unfair" to label the group as "radical," reports Australia's The Daily Telegraph. Although he acknowledged that the group takes a hard line on moral issues, such as prostitution and gambling, he argued that they did not support violence, especially terrorism.

"I think there is a need for the international community to be fair in labelling Islamic movements as radical, especially in Indonesia," Mr. Gymnastiar said.

"It hurts our feelings if there is a label from outside as a radical group. From a close distance ... they don't have radical strategy or proposal for social change."

Indonesian officials prohibited a prominent member of Hizb ut-Tahrir's Australian branch from entering the country to speak at Sunday's event, as well as the party's British representative. Also, Abu Bakar Bashir, a radical cleric, received an "ultimatum" from police prohibiting him from speaking at the event, reports Australia's Herald Sun.

"We don't know why exactly, what is the real reason why they were deported," said the group's Indon spokesman Ismail Yusanto. "They came to Indonesia with a goodness."

Al Jazeera reports that critics have said an official adoption of sharia law would be "detrimental to the world's most populous Muslim nation." Azyumardi Azra, who works at the State Islamic University in Jakarta, went so far as to say that the implementation of sharia in Indonesia is illegal and that the nation's supreme court must make this clear.

"Introducing sharia bylaw is threatening to development, so that's why I appeal from time to time to the Supreme Court to investigate the so-called Sharia bylaw," Azra said, speaking to Al Jazeera.

Since the nation declared its independence from the Netherlands in 1945, there has always been talk of implementing sharia law in Indonesia. During the drafting of the nation's Constitution there was talk of adding a clause to the principle of Pancasila, or belief in one supreme God, that would require Muslims to live by sharia. However, it was quickly dropped from the draft, reports The Jakarta Post. The chairman of Muhammadiyah, an Islamic organization in Indonesia, said that any implementation of a caliphate – or khilafah in Arabic – would have to conform to the state ideology of Pancasila.

"Khilafah shouldn't undermine the inclusivism and pluralism of the nation," said [Din Syamsuddin, the chairman].

He added that non-Muslims did not have to be afraid of the discourse on Khilafah as it was part of the democratic process.