UPDATE 1-Fiat signs deal to supply light vans to Opel

* Fiat to produce successor of Cosmo model at Turkish plant

* Aims to produce more than 250,000 units

* New light van to be build on Fiat Doblo platform

(Adds detail, background)

MILAN, Nov 29 (Reuters) - Fiat FIA.MI has signed a deal with Opel GM.N to supply at least 250,000 units of a new light van from a Turkish plant the Italian carmaker jointly operates with Koc Holding KCHOL.IS under the Tofas venture.

The deal, the first of this kind between Fiat and Opel, is one of many accords global carmakers are signing to rationalise production in the face of diminishing demand in mature markets.

The vehicles will succeed Opel’s Combo model and be produced on Fiat’s existing platform for its Doblo van. They will be sold by Opel and Vauxhall dealers in Europe and other markets outside North America from 2012.

Under the terms of the deal, Fiat will start supplying 6,000 vehicles to Opel in December 2011 with a view to hiking production to “at least 250,000 units”, Fiat said on Monday.

Fiat currently produces more than 100,000 Doblo vans a year at the Turkish plant. Buoyant sales of light commercial vehicles were one of the drivers of forecast-beating third-quarter results at Europe’s sixth-largest carmaker.

Opel is the European arm of U.S. carmaker General Motors. (Reporting by Lisa Jucca; Editing by Dan Lalor)