(Adds security source)

JERUSALEM, July 6 (Reuters) - Israel has arrested Jewish suspects in the abduction and killing of a Palestinian teen whose death touched off violent protests in Jerusalem and in Israeli Arab towns, a security source said on Sunday.

Six suspects were in custody, the source said, but added the number may change as the investigation into the killing of Mohammed Abu Khudair, 16, progressed.

The source gave no other details about the suspects other than to say they were Jews. There was no official comment from the police.

Investigators believe Mohammed Abu Khudair was slain out of "nationalist motives", the source said, in comments that appeared to confirm Palestinian suspicions that far-right Jews were involved and that his death was a vengeance killing.

Abu Khudair's burnt body was discovered in a Jerusalem forest on Wednesday, a day after the burial of three Jewish teens who were abducted while hitchhiking in the occupied West Bank on June 12.

Their bodies were found on Monday, near the road where they had gone missing, and Israel blames Hamas militants for their kidnapping and killing. The Islamist group has neither confirmed nor denied involvement.

Palestinians have clashed with Israeli police in Jerusalem over the past several days. The violence spread on Saturday to Arab towns and villages in central and northern Israel.

The areas were largely quiet on Sunday, but police remained on high alert. (Writing by Jeffrey Heller Editing by Ori Lewis and Mark Potter)

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