LONDON:  Leading electric carmakers may be unwittingly using child labour to produce batteries for vehicles that have grown in popularity for using clean energy aimed at limiting global warming, Amnesty International said on Friday.

The human rights watchdog said cobalt used in lithium ion batteries for electric vehicles, phones and laptops could come from mines in Democratic Republic of Congo (DRC) that use child labour.

It accused carmakers including GM, Renault-Nissan, Fiat Chrysler, Volkswagen, Daimler and Tesla of failing to map the supply of cobalt from mines in Congo to smelters and on to battery-makers.

As a result, electric cars sold across the globe could contain traces of the metal produced each year by informal Congolese mines without companies knowing, the group said.

"We have found that there is significant risk that cobalt mined by children could be entering their supply chains," said Mark Dummett, human rights researcher at Amnesty.

Due to the growing demand for lithium ion batteries in electric cars and consumer goods like mobile phones, Dummett said carmakers had an obligation to trace their supply chain to ensure children were not used to mine cobalt.

"Frankly companies owe it to their consumer to be transparent about their supplies and to map out their supply chains so that they know where it's coming from," he said in an interview with the Thomson Reuters Foundation.

More than half of the world's cobalt comes from DRC, Amnesty said, and 20 percent of the mineral was mined by hand.

Millions of Congolese work in informal mining, with rudimentary tools and usually without legal authorization. They often scavenge in the waste heaps of larger mines.

Congo's supply of metals such as tantalum, tin, tungsten and gold has been under scrutiny since 2010, when laws in the United States required U.S.-listed companies to ensure their supply chain was free from these so-called "conflict minerals".

But cobalt has received scant regulatory attention, although Congo, where dozens of armed groups roam its lawless eastern region, is the source of more than half of global supply.

SUPPLY CHAINS

Europe's biggest carmaker Volkswagen (VW) told the Thomson Reuters Foundation it was investigating whether cobalt in their electric car batteries was mined in DRC.

"To our best knowledge, the cobalt in our batteries does not originate from the respective sources from DRC. To our best knowledge we had no human rights abuses in our cobalt supply chain," VW spokeswoman Leslie Bothge said.

Electric carmaker and energy storage company, Tesla said there was "very little" cobalt in its batteries, adding that going deep into their supply chain to investigate the use of child labour was "both unusual and challenging".

"We have asked the company in the DRC that produces this trace amount of cobalt deep down within our supply chain to provide written documentation directly to us concerning their practices," Tesla spokesman Alexis Georgeson told the Thomson Reuters Foundation.

"That documentation confirms that child or compulsory labour or human trafficking are prohibited."

GM said in a statement it has a "zero-tolerance policy" on child labour and other unethical business practices, requiring written compliance from its suppliers.

Mercedes maker Daimler also told the Thomson Reuters Foundation it was investigating the "processes and measures taken by our suppliers to prevent such alleged practices in their upstream supply chains."

But Amnesty's Dummett said although many electric carmakers had human rights policies, they were not willing to publicly disclose the steps they were taking, if any, to actively prevent child labour in their supply chains.

CLEAN ENERGY

Electric car prototypes and plans are growing in popularity, and dominating this year's Paris auto show, as falling battery costs persuade executives and investors that plug-in vehicles are ready to go mainstream.

The Climate Action Tracker, a leading body that monitors government actions on climate, said the last gasoline-powered car will have to be sold by about 2035 to put the world on track to limit global warming.

Last December, world leaders at a Paris summit set a goal of limiting a rise in temperatures to "well below" 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times while "pursuing efforts" for a much tougher 1.5 C (2.7F) ceiling.

"We're not saying people shouldn't buy these electric cars," said Dummet.

"But consumers who buy them should expect that these hugely wealthy companies ... absolutely have the capacity to do this due diligence to map out their supply chain."