Three of six Israelis held over the abduction and killing of a Palestinian teenager last week have confessed to the murder, a source close to the investigation said on Monday.

"Three out of six suspects in custody have confessed to the murder and burning of Mohammed Abu Khder, and performed a re-enactment of the crime" in front of officers, the source told AFP, requesting anonymity.

Israel arrested six Jewish extremists on Sunday in connection with the killing of 16-year-old Abu Khder on July 2, in a gruesome attack that triggered days of clashes in annexed east Jerusalem and Arab Israeli towns.

Initial autopsy findings from the body of Abu-Khedr, who Palestinians believe was kidnapped and killed by far-right Jews, showed that he was burned alive, the Palestinian attorney-general was reported as saying on Saturday.

The attack is believed to have been in revenge for the kidnap and murder of three Israeli teenagers in the occupied West Bank last month, and the twin attacks have ratcheted up tensions throughout Israel and the Palestinian territories.

Authorities have placed a gag order on most aspects of the investigation into Abu Khder's murder.

But Honenu, a legal organisation which defends right-wing Jewish extremists, said it was representing six people -- three of them minors -- whose remand was extended by the Petah Tikva magistrates court, just outside Tel Aviv, on Sunday.

The confession reports came hours after Benjamin Netanyahu, Israel's prime minister, spoke to the father of Abu Khdeir, and promised to bring his killers to trial.