(Adds JI leader's sentence)

JAKARTA, April 21 (Reuters) - An Indonesian court sentenced two top leaders of the regional Jemaah Islamiah (JI) militant group to 15 years each in prison on Monday for harbouring militants and for weapons possession.

Abu Dujana, the military chief of the group, was arrested in June on charges of keeping explosives and sheltering fugitives wanted for a series of deadly attacks in the country in recent years.

Zarkasih, who was arrested only days after Dujana, was the alleged amir, or leader, of the group from 2005 through 2007.

Their arrests were regarded as a major blow for the group, blamed for the 2002 Bali bombings in which more than 200 people were killed, as well as many other attacks in Indonesia.

The chief judge, Wahjono, said Dujana had been sentenced to 15 years for rifles and ammunition possession and funding and harbouring other group members.

The judges also sentenced Zarkasih to 15 years for his membership in JI and "evil conspiracy in terror activities".

An earlier charge sheet said that Zarkasih, nicknamed Mbah, or grandfather in the Javanese language, had received military training in Pakistan in the late 1980s and taught map reading at a Muslim rebel camp in the southern Philippines in 1998.

Dujana and Zarkasih have denied any role in attacks blamed on JI, which the panel of three judges said was a "terrorist" organisation.

Police in several countries have linked JI to al Qaeda but Indonesian authorities have argued they cannot ban the group since it is not a formally established organisation.

Although several key strategists and bomb experts in JI have been captured or killed, some analysts say it and its splinter groups still have the capacity to launch attacks.

Indonesia is the world's most populous Muslim country. While the vast majority of Muslims are moderate, the country has seen the emergence of an increasingly vocal militant minority. (Writing by Olivia Rondonuwu; Editing by Sugita Katyal and Sanjeev Miglani)

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