A Thai news website says one of its journalists was detained by police in central Thailand while reporting on a group opposed to the military government. It says three activists of the group were also detained.

Prachatai said in a report on its website that journalist Taweesak Kerdpoka was arrested Sunday while reporting on the New Democracy Movement in Ratchaburi province. It said the four were detained after police searched the activists' car and found copies of the group's booklet.

It says the booklet provides "counter information" to the junta's position on a referendum it plans to hold Aug. 7 on a new draft constitution that has been criticized by many as undemocratic.

Taweesak is the first journalist to be arrested under a new law criminalizing criticism of the referendum.