LONDON (Reuters) - British motor insurer Admiral said it had negotiated a deal to share the risks it takes on at its new US operation, and had extended similar agreements already in place at its European businesses.

Cardiff-based Admiral, which insures about six percent of the cars on Britain's roads, said reinsurers Munich Re and Hannover Re had each agreed to take on one third of the risks it underwrites in the US.

The company also said it had extended its existing reinsurance deal in Britain with Munich Re by two years to 2016 and had prolonged its contracts with the company in Spain and Italy.

Munich Re, which holds more than 10 percent of Admiral's shares, will take a 40 percent share of the company's British insurance book for each of the additional two years, compared with 45 percent in 2010.