Robert Go, Jakarta – Concern is growing in Jakarta that President Abdurrahman Wahid's supporters may take matters into their own hands and act against the leader's detractors, including top legislative assembly speaker Dr Amien Rais.

Mr Abdurrahman, in his regular Friday afternoon prayers address, asked his supporters to remain calm and avoid violent situations. "If I can be patient, those under me should also be able to maintain self-control," he said. The President, through a statement released mid-week, had asked Indonesians "not to respond too emotionally to developments in the political situation".

Speaking on a separate occasion, presidential spokesman Wimar Witoelar said on yesterday: "There is a serious worry [that] the President's supporters might lose their tempers and attack those who criticise him."

Mr Muhaimin Iskandar, a legislator from the President's Nation Awakening Party (PKB), advised Mr Abdurrahman and Dr Amien to stop criticising each other. "The leaders should know how the people could easily act out their frustrations. So they should aim to defuse tension," he said. Mr Muhaimin also argued that the authorities, including Mr Abdurrahman, would be hard-pressed to stop such a civil clash once it starts.

The remarks came amid heightening tension in some parts of the country between Mr Abdurrahman's and Dr Amien's respective grassroots bases, the country's two largest Muslim groups Nahdlatul Ulama (NU) and Muhammadiyah.

Last Wednesday, a crowd estimated at 10,000, led by a group of young NU leaders, took to the streets of Pasuruan – a small town in East Java – to declare their support for Mr Abdurrahman.

The demonstration was largely peaceful, but the crowd chanted threats against Dr Amien, who plans to visit the province later this month, and waved aloft posters promising:"If Gus Dur and Mega go down, Muhammadiyah will be destroyed."

Muhammadiyah leaders and members of Dr Amien's National Mandate Party (PAN) have expressed regret over the NU faction's threats, but declined to elaborate on the issue.

"It is regrettable that the President's people are getting so emotional about this democratic process that they threaten violence," said Mr Joko Susilo, a PAN legislator and head of Muhammadiyah's youth wing.

Dr Amien, who has publicly declared his own ambitions for Indonesia's top job, was one of Mr Abdurrahman's allies during last October's presidential election, but has since turned into the administration's harshest critic this year.