The sons of murdered journalist Jamal Khashoggi have asked Saudi Arabian authorities to return the body of their father so the family can properly grieve.

Mr Khashoggi was killed inside the kingdom's consulate in Istanbul by a team sent from Riyadh on 2 October, a murder Turkey's president said was ordered from "the highest levels" of Saudi Arabia's government.

"I really hope that whatever happened wasn't painful for him, or it was quick. Or he had a peaceful death," Abdullah Khashoggi told CNN during an interview in Washington.

His brother Salah said "all what we want right now is to bury him in Al Baqi in Medina with the rest of his family," referencing a cemetery in Saudi Arabia.

"I talked about that with the Saudi authorities and I just hope that it happens soon."

Turkey's chief prosecutor said recently that Mr Khashoggi was strangled as soon as he entered the consulate and also confirmed the body was dismembered.

An advisor to Turkish President Recep Tayyip Erdogan, hinted in an article published on Friday that the body may even have been destroyed in acid.

Mr Khashoggi's killing has provoked widespread outrage and sharp criticism from Washington, usually the staunchest of allies.

Mr Khashoggi's sons voiced worry that the work of their father, a columnist for The Washington Post, was being distorted for political reasons.

"I see a lot of people coming out right now and trying to claim his legacy and unfortunately some of them are using that in a political way that we totally don't agree with," Salah told CNN. "My fear is that it's being over politicised."

"Jamal was never a dissident. He believed in the monarchy, that it is the thing that is keeping the country together."

The brothers said they have relied primarily on news reports to piece together an understanding of their father's death.

"There's a lot of ups and downs....We're trying to get the story, bits and pieces of the story to complete the whole picture," Abdullah said. "It's confusing and difficult."

"It's not a normal situation and not a normal death."

Salah emphasised that "the King has stressed that everybody will be brought to justice. And I have faith in that."

In a separate development, a senior Turkish official has said Saudi Arabia sent a toxicologist and a chemicals expert to Istanbul to cover up the murder before the Turkish police searched the kingdom's consulate.

"We believe that the two individuals came to Turkey for the sole purpose of covering up evidence of Jamal Khashoggi's murder before the Turkish police were allowed to search the premises," the official said on condition of anonymity.

The murdered journalist's fiancée, meanwhile, has called on US President Donald Trump to back Turkey's efforts to probe the death.