The arrest of Abu Dujana, believed to head a special forces unit within Jemaah Islamiyah -- which has been linked to al-Qaeda -- is a major breakthrough for Indonesia's efforts to curb the activities of the group.

Dujana, 37, was among suspected militants detained in a series of weekend raids carried out by Indonesia's anti-terror unit, Detachment 88, police spokesman Sisno Adiwinoto told a press briefing.

"The person that was arrested on Saturday, Yusron Mahmudi, has many aliases and one of them is Abu Dujana," Adiwinoto said, adding that he was known under at least six names.

Abu Dujana "is known to be more important than Noordin M. Top or Azahari Husin," he said, referring to two Malaysian members of JI.

Azahari was killed by Indonesian police in a raid in November 2005 while Noordin Muhammad Top, who has been described as Southeast Asia's most wanted man, remains on the run.

Police had originally said they believed Yusron was an aide to Dujana, believed to have been tasked with collecting weapons and explosives for JI.