The detainees, whom the government alleges are members of a group allied to the Jemaah Islamiyah organisation, were arrested in 2001 under a strict security law that allows indefinite detention without trial on government orders renewable every two years.
The prisoners want a high-ranking Home Ministry official to meet them to discuss terms for their freedom, lawyer Ahmad Sabki Yusuf said.
"They are very weak and can hardly speak," Ahmad said after visiting the suspects in the Kamunting prison camp in northern Malaysia.
Sixteen suspects began fasting on Monday to protest their detention without trial, but two of them became dangerously dehydrated and were sent to a hospital Tuesday, Ahmad said. One returned to the camp on Wednesday and resumed fasting.
Sam Zia-Zarifi, the deputy director of New York-based Human Rights Watch's Asia Division, urged the Malaysian government to allow independent organisations to monitor the detainees' condition.
"The Malaysian government is responsible for the life and well-being of the detainees," he said in a statement.
Authorities claim the suspects belong to the Malaysian Militant Group, or KMM, which regional officials say has links to Jemaah Islamiyah, the network blamed for the bombings on Indonesia's Bali island in 2002 and at the JW Marriott hotel in Jakarta in August.
But the KMM suspects have not been directly linked to those attacks, and were arrested before Malaysian and Singapore authorities broke up an alleged Jemaah Islamiyah plot to blow up the US and other Western embassies in Singapore in late 2001.
"The Malaysian government is responsible for the life and well-being of the detainees"
Deputy director of New York-based Human Rights Watch's Asia Division
Twenty-seven other detainees, all of whom are allegedly Jemaah members, have also stopped consuming food since Monday in a show of solidarity with the main group of fasters. However, they are still taking water and remain healthy, Ahmad said.
In total, more than 70 suspects are jailed under the security law in Malaysia.