Hyundai Motor Co and affiliate Kia Motors Corp plan to triple their number of fuel-efficient cars by 2020, addressing concerns about the pair's green track record and competitiveness in fuel economy.

Investors have voiced concern about Hyundai's latest Genesis and Kia's Soul having lower fuel mileage than their predecessors, and about a $350 million fine in the United States for overstating vehicles' fuel economy.

The announcement on Wednesday came a week after the pair pledged to raise the fuel economy of their vehicles by 25 per cent by 2020 to meet emissions regulations in the United States and Europe and at home in South Korea.

It also followed an announcement on Tuesday that the pair would buy back 670 billion won ($615 million) worth of shares, in what was widely regarded as an attempt to appease investors angered by a $10 billion bid for property for new headquarters.

"Investors have complained about Hyundai's lack of shareholder-friendly policies and communication about its vision, especially after the land deal," said analyst Yim Eun-young of Samsung Securities.

"Today's announcement seems to be part of its efforts to soothe shareholders and better communicate with the market."

Shares of Hyundai have fallen 25 per cent this year, but have risen over 17 per cent since hitting a more than 4 year low on Nov. 5. Kia stock has declined 0.9 per cent while the benchmark index has lost 2.4 per cent.

Under Wednesday's plan, Hyundai and Kia will raise their number of fuel-efficient cars to "at least" 22 by 2020 from seven now.

"We have set an internal target of making it to No.2 in the global eco-friendly car market, which is expected to grow from this year's 2.2 million vehicles to 6.4 million in 2020," Hyundai said in a joint statement with Kia.

Hyundai and Kia plan to release 12 models powered by gasoline-electric hybrid engines, expanding the line-up to small cars and sport utility vehicles.

The pair's green range will also have six plug-in hybrid mid-sized and compact cars, two fuel-cell cars and two battery-powered electric cars. – Reuters