Among those arrested last week was Ambo Intang, who was sought for his alleged involvement in the 2012 killings of two policemen in in the Central Sulawesi district of Poso, said national police spokesman Maj. Gen. Ronny F. Sompie.
An anti-terrorism police squad has earlier nabbed two other suspects. One of them was identified as Bambang Aribowo, who was arrested upon arrival at Jakarta's airport.
Sompie said police intercepted a shipment containing two homemade bombs that was sent from East Java town of Trenggalek to Makassar. The bombs were to be used to attack brothels in the province, Sompie said.
Indonesia, the world's most populous Muslim nation with a secular central government, has been battling terrorists since 2002, when militants linked to the Southeast Asian network Jemaah Islamiyah began attacking Western nightclubs, restaurants and embassies. Their mostly deadly attacks by far were at Bali nightclubs in 2002, killing 202 people, mostly foreign tourists.