Daimler will unveil a new version of the Mercedes-Benz Pullman at next month's Geneva auto show, a six-seater stretch limousine known in the past for its popularity with plutocrats, dictators and politicians.

Also expected is a plug-in hybrid version of its popular C-Class sedan, the first among a raft of vehicles to be sold with a partially electric drivetrain which allows for zero-emission driving in town traffic.

The Pullman is based on the Mercedes-Benz S-Class, but will have a wheelbase which is a full meter longer than the standard version to allow for an extra row of seats, the German luxury carmaker said.

The original Pullman 600, launched by Mercedes-Benz at the Frankfurt auto show in 1963, was over 6 meters long and had a top speed of 200 kilometers per hour (124 mph).

It gained notoriety in some circles as a "dictator ship" because it proved so popular with autocrats including Uganda's Idi Amin, Romania's Nicolae Ceaucescu, and Yugoslavia's Josip Broz Tito.

The new version is designed to allow high-level dignitaries to continue face-to-face discussions thanks to a row of rear-facing seats.

In April, Reuters reported that Mercedes-Benz was working on a Pullman "state limousine" which is set to cost up to $1 million in its armor-plated version.

The original Pullman had a complex hydraulic suspension that allowed it to hurtle along at high speeds on bad quality roads.

At the time, Mercedes wanted to show rivals Rolls-Royce and Cadillac it could make a car that was comfortable even at high speeds, a difficult feat for armor-plated vehicles weighing over 3.4 tonnes.