Wednesday marked 20 years since bombings in Indonesia's Bali killed more than 200 people. People gathered at a ceremony to mark the tragedy near the locations where the attacks occurred.

Victims' families offered flowers and letters. A monument bears the names of all those killed.

One bomb survivor said, "The incident has caused me psychological trauma. I get a headache whenever I smell smoke."

Massive explosions ripped through nightspots packed with tourists in the Kuta area on October 12, 2002.

More than 200 people from 22 countries and territories died. The Jemaah Islamiyah terrorist group was blamed for the bombings.

Police arrested several members of the group, including one of its top members. Authorities executed three of the masterminds in 2008.

A group member who made the bombs used in the attack spoke with NHK through a video link. Ali Imron has been in prison since receiving a life sentence in 2003. He took a de-radicalization program provided by the government.

He said it took a long time to rid himself of the kind of radical thinking held by a terrorist.

He said, "I can only apologize to the victims. There's nothing else I can do. I'm now making efforts to prevent another tragedy like the Bali bombing, through a program with the police to de-radicalize people who have the wrong ideas of jihad."

Indonesia continues to face terror threats. The Islamic State group and others have targeted police buildings and Christian churches.

A top official of the National Counter-Terrorism Agency warns that radical ideas can easily spread through social media and reach the younger generation.

He says terrorists raise public funds in the name of humanitarian activities but use the money to help movements that employ violence.

National Counter Terrorism Agency head Boy Rafli Amar said, "Terrorists don't stay still. They don't stick to the old ways but introduce new approaches. We need to come to terms with the fact that the potential threat of terrorism will never stop, because efforts to spread the ideologies behind terrorism continue."

Police have been stepping up measures against terrorist groups by creating special-forces units. The Jemaah Islamiyah terrorist group is in decline, but authorities remain on alert.