The Metropolitan Police is assessing new information it has recently received about the deaths of Princess Diana and Dodi Al Fayed in 1997.
Scotland Yard said it was "scoping" the information and "assessing its relevance and credibility".
It said it was "not a re-investigation" into the deaths of the couple in a Paris car crash on 31 August 1997.
An inquest in 2008 found they had been unlawfully killed, partly due to the "gross negligence" of their driver.
In a statement on Saturday evening, the Metropolitan Police said the assessment would be carried out by officers from the specialist crime and operations command.
It added that the deaths had been "thoroughly investigated and examined" by the inquest held at the Royal Courts of Justice in London.
Reports in several British Sunday newspapers suggest there are allegations the military was involved and that information had been passed to the police by an Army source.
A Met Police spokesman said that the force would "not discuss the source of the information" it was assessing.
A royal spokeswoman also said there would be no comment on the matter from Prince William or Prince Harry, or from Clarence House.
A spokesman for Dodi's father Mohamed Al Fayed said he had no comment to make, but said he would be "interested in seeing the outcome", adding that he trusted the Met to investigate the information "with vigour".
Paparazzi on motorbikes
Scotland Yard said its assessment did not come under Operation Paget - the police investigation into allegations that the princess and Mr Al Fayed, her boyfriend, were murdered.
It was a theory endorsed at the time by Mohamed Al Fayed, the then owner of London store Harrods.
But in December 2006, the report into Operation Paget said it had found no evidence of murder and dismissed all conspiracy theories surrounding the deaths.
Operation Paget concluded, just like the French investigation in 1999, that driver Henri Paul had been drunk and driving at excessive speed.
Dai Davies, a former head of royal protection, told ITV news the deaths were "an accident by any definition, and three separate inquiries... have come to the same independent conclusion".
He added: "I am absolutely convinced this was an accident so I'm mystified, after 13 years, how any new information can possibly allege anything other than that this was a tragic accident."
Princess Diana, the former wife of the Prince of Wales and the mother of Princes William and Harry, was 36 when she died alongside Mr Al-Fayed, 42.
Mr Paul was driving when their hired Mercedes crashed into a pillar in Paris's Pont de l'Alma tunnel.
The crash happened after the couple had left the Ritz Hotel and were pursued by paparazzi on motorbikes. Mr Al-Fayed's bodyguard, Trevor Rees-Jones, was the only survivor.
At the inquest into their deaths, the jury found the couple had been unlawfully killed and the deaths were the result of "gross negligence" on the part of Mr Paul and the paparazzi.
The paparazzi pursuit, Mr Paul's drink-driving and a lack of seatbelts contributed to the deaths, the jury said.
The inquest lasted more than three months and heard from 250 witnesses.
After the hearing it was announced that its cost had reached £4.5m, with a further £8m spent on the Metropolitan Police investigation.