Indonesian police said today they have arrested two members of the regional Islamic militant network Jemaah Islamiah -- the leader of the group's Singapore branch and a suspect in October's nightclub bombings on the resort island of Bali.

Mas Selamat Kastari, wanted in Singapore for alleged participation in a hijacking plot, was arrested Sunday on the Indonesian island of Bintan, a short ferry ride from Singapore's southern coast, said Erwin Mappaseng, head of the Indonesian criminal investigation department.

Kastari, a Singaporean who fled the island city-state in December 2001, planned to hijack a U.S., British or Singaporean jetliner flying out of Bangkok and crash it into Singapore's Changi Airport, Mappaseng said.

National Police spokesman Didi Rochyadi said a Malaysian named Noor Din, suspected of helping plan the blasts last October on Bali that took almost 200 lives, was arrested early today in the town of Gresik on the eastern part of the island of Java.

During Noor Din's arrest, police seized an M-16 rifle and ammunition that belonged to a Bali suspect, Ali Imron, who is already in custody, police said.

The arrests are evidence of Indonesia's political will to shut down the regional terrorist network and to pursue suspects beyond the Bali case, said Zachary Abuza, a Southeast Asia terrorism expert who teaches at Simmons College in Boston.

Indonesian police have arrested 29 suspects in connection with the Bali attack, which they have said was executed by Jemaah Islamiah. But several key suspects are still at large, including the group's operational commander, an Indonesian who goes by the single name Hambali and is also known as Riduan Isamuddin.

Kastari has not been named a suspect in the attack.

Announcement of the arrests came on a day that a bomb exploded at the National Police headquarters, demonstrating that terrorists continue to operate in Indonesia. No one was killed or injured.

The National Police chief, Dai Bachtiar, said in parliament, "I am sure there is some sort of political message" in the early morning bombing.

A security analyst in Jakarta speculated that the incident was linked to the detention at the headquarters of Abubakar Baasyir, an Indonesian Muslim cleric who intelligence analysts contend heads Jemaah Islamiah.

Baasyir was arrested in October in connection with a plot to kill President Megawati Sukarnoputri and conduct a string of church bombings in December 2000.

Police two weeks ago extended his detention to March 1, his attorney said. He was moved to the police headquarters in December.