Kia is looking at introducing diesel engines to America as part of its long-term plan to continue growing by entering new segments.

The arrival of the K900, a Mercedes S-Class-sized luxury saloon, in the US in February and the launch of the company's first commercially available all-electric car, the Soul EV, towards the end of this year are two pointers as to how Kia is expanding its range to appeal to new customers.

And the company now sees potential for diesel in the traditionally hostile US market - although not for another three or four years.

"The problem right now is that there are different emissions standards in Europe and the US, which means we would be faced with different after-treatments, and that makes it very expensive," says Orth Hedrick, the vice-president of product planning for Kia Motors America.

"But with EU6 in 2017-18 there would be the same standards in both Europe and the US, and that gives us a better chance." Hedrick insists that no decision has been taken, but is encouraged by the progress German manufacturers are making at converting Americans to diesel - even if they are offering dealers and buyers support to do so.

The US has now overtaken Kia's domestic market, Korea, as the brand's top-selling region, and is by far its most profitable sales area because of the upmarket models which dominate. Kia sold more than 500,000 cars in the US in 2013, including 100,000 Sorento SUVs and a similar number of Optima saloons, both of which are produced locally.

The company enjoyed its best-ever half-year in the US between January and June 2014, with 297,500 sales, including a record month in May, when it sold 60,000 cars.