Singapore has arrested 21 people, most of whom belong to a regional Islamic group that authorities here have linked to Al Qaeda, the government said Monday.

All the suspects were arrested in August and are Singaporean citizens, according to media statement by the Ministry of Home Affairs.

The statement said most of the men were from Jemaah Islamiyah, a group that authorities in Singapore say had planned to attack U.S. interests there. Some of the men had received military training in Afghanistan and at a training camp of the Moro Islamic Liberation front in the southern Philippines, it said.

More than a dozen members of the group have already been arrested.

"These latest arrests have seriously disrupted the JI (Jemaah Islamiyah) network in Singapore, the statement said.

The arrests were made under Singapore's Internal Security Act, which allows for indefinite detention.

The arrests were made as a result of investigations conducted after the arrests of 13 group members in December, it said.

A number of the men were arrested in December allegedly instructed the men arrested last month to conduct "reconnaissance and surveys of select targets in Singapore," the government statement said.

The statement gave few other details, but planned to release more later.

Singapore has been one of Southeast Asia's most cooperative countries in the war on terror.