Palestinian protesters run away from tear gas fired by Israeli soldiers during clashes.  -Reuters

AFP/Ramallah

A Palestinian teenager whose abduction and murder set off violent protests was burned alive, according to initial autopsy reports, as clashes over the incident spread on Saturday from east Jerusalem to Arab Israeli towns.

Mohammed Abu Khder, 16, was abducted from his Shuafat neighbourhood in occupied east Jerusalem early Wednesday and his charred body found not long after in a west Jerusalem forest.

Palestinians said it was the deed of Jewish extremists in revenge for the kidnapping and murder in the West Bank last month of three Israeli teenagers

Palestinian news agency Maan quoted Attorney General Mohammed Aluweiwi Saturday as saying the initial findings of a post-mortem indicated the presence of smoke in the boy's lungs, meaning he was still alive while he was being burned.

Abu Khder also suffered a head wound, but that did not cause his death, Aluweiwi added.

Israeli police said Saturday they still could not confirm the motive for Abu Khder's murder.

A spokeswoman told AFP police were investigating "all possibilities," and that there was a gag order on all details of the investigation.

The teenager's funeral Friday, joined by thousands of mourners, was accompanied by clashes across Israeli-annexed Arab east Jerusalem, the third straight day of violence since the discovery of his body.

Disturbances spread to the Arab towns of Taibe in northeastern Israel and Jaljulia and Qalansuwa in the centre where one car was torched after its Jewish owner was pulled out of it, police said.

More a dozen Arab Israelis were arrested, they added.

Police said they remained on high alert Saturday ahead of further possible clashes.

- Murdered teen's cousin arrested -

One of those arrested in the east Jerusalem clashes was Tariq Abu Khder, the 15-year-old cousin of the murdered Palestinian youth and an American citizen on vacation in east Jerusalem.

Speaking to AFP Saturday, his parents said Tariq was arrested in Shuafat after being beaten by police on Thursday.

A video circulated on social media (https://www.youtube.com/watch?v=HDENWwEDGr4) shows what appears to be Israeli border police beating and kicking a handcuffed semi-conscious figure before dragging him away.

The parents, who saw their son in an Israeli hospital, said they were told Tariq was arrested for being masked.

Police spokeswoman Luba Samri could not confirm it was Tariq in the video, but said the footage was from the arrest of a group of six Palestinians, of which Tariq was part.

Samri said police found a sling on Tariq, who attacked police and resisted arrest, while others were stoning the police force and throwing Molotov cocktails at them.

Samri said six police were wounded during that arrest operation.

Abu Khder will appear before a Jerusalem court Sunday, his parents said.

Meanwhile, militants continued rocket and mortar fire at Israel from Gaza on Saturday, amid Egyptian efforts to broker a renewed truce between Israel and its foe Hamas following a flare-up of cross-border violence.

Ten rockets and mortar rounds were fired at southern Israel, the army said, with one soldier lightly wounded by mortar fire.

There has been a surge in militant rocket fire and retaliatory Israeli air raids since the kidnapping and murder of the three Israeli teens prompted a huge Israeli crackdown on Hamas in the occupied West Bank.