Israeli President Reuven Rivlin on Sunday formally rejected a request to pardon a soldier convicted of manslaughter for shooting dead a prone Palestinian assailant, Rivlin's office said.

"President Reuven Rivlin today took the decision to deny the request for pardon filed by Elor Azaria," it said in an English-language statement, exactly one month after the jailed soldier submitted his request.

On July 30, a military court turned down Azaria's appeal against his conviction for manslaughter and upheld an 18-month prison sentence, which he began serving on August 9.

In September, Israel's Chief of Staff General Gadi Eisenkot reduced the term by four months.

Amnesty International has said Azaria's sentence does "not reflect the gravity of the offence".

The UN human rights office said it was an "unacceptable" punishment for "an apparent extra-judicial killing".

However, both Prime Minister Benjamin Netanyahu and Defence Minister Avigdor Lieberman have supported a full pardon.

The written reply to the pardon application, quoted in Sunday's statement, says that Rivlin noted Eisenkot's clemency and the court's "lenient" sentence.

"The President learned that in passing sentence, the military court took into account the circumstances raised by you... as consideration of leniency, and he noted it took them into account in passing a lighter sentence," it said.