Secret agents from the MI6 intelligence agency are to testify at the inquest into the deaths of Princess Diana and partner Dodi Fayed.

In the hearing scheduled for Tuesday, the secret agents will be identified only by letters such as 'X' or 'H' and the court will be closed to members of the public and media.

The agents are expected to testify about a proposal to assassinate a Balkan leader.

Former MI6 chief Richard Dearlove testified last week that the idea was quickly "killed stone dead" and denied any MI6 involved killings during his time as director of special operations and head of the agency.

Former MI6 agent Richard Tomlinson has claimed that he saw a plan to kill the late Slobodan Milosevic when he was president of Serbia in a car accident - but now says he may have been wrong about the target and the method.

Fayed's father, Mohamed al-Fayed, has claimed that the plan reported by Tomlinson was the blueprint for killing his son and the princess.

The inquest into Princess Diana and Dodi al-Fayed's death opened last October and was expected to last six months. Numerous witnesses and royal aides have testified in the hearing.