On Sunday police used water cannon and tear gas to break up a protest by up to 10,000 ethnic Indians who took to the streets of Malaysia's largest city, Kuala Lumpur, to call for equal rights.
Some 80 protesters have since been charged with illegal assembly after participating in the banned rally.
Other protest leaders have said they also expect to be arrested following Ganapathy's detention on Thursday.
P Uthayakumar, a co-founder of Hindraf, told The Associated Press that police gave no reason for the arrest, adding that police may come for him and his brother, P Waytha Moorthy, next.
|Abdullah said future protesters could face |
indefinite detention without trial [AFP]
"I'm prepared for the worst. I'm standing up for a principle.... We are left with no choice but to fight," Uthayakumar said.
The latest moves come after Malaysia's prime minister threatened to use the Internal Security Act which allows for indefinite detention without trial to prevent future protests.
Abdullah Ahmad Badawi said the ISA, first introduced in the colonial era, would be used to avert "untoward incidents that can harm the prevailing peace and harmony and create all sorts of adverse things".
"When it is appropriate to use it, it will be used," he said.
Indians, comprising about seven per cent of Malaysia's 27 million people, say government policies discriminate against them in favour of ethnic Malays in jobs, education, business and government contracts.
The ethnic Chinese who make up a quarter of the population are generally wealthier than the Indians, most of whom earn low wages and work in menial jobs.
The government has denied such claims, accusing Hindraf of trying to create racial animosity.
It banned Sunday's protest saying it could inflame racial tensions.
Rights groups who have campaigned to have the ISA abolished cautioned the prime minister against using such preventive detention laws.
T Kumar, Amnesty International's Asia-Pacific advocacy director in Washington, said it was "a huge mistake" to consider the ISA and urged Abdullah against using it.