Apple is extending its supply chain clean up beyond Chinese factories and into African mines, using name-and-shame tactics to cut the amount of"conflict minerals" that end up in its iPhones and iPads. As it touts fresh improvements to working conditions in the factories that produce its devices, the world's most valuable technology company is now combining its might in electronics-component purchasing and marketing to pressure smelters to make their sourcing more ethical. (Read more: Apple drops5% on weak iPhone sales, revenue outlook)

Apple employees walk towards the Apple Headquarters in Cupertino, California. Kimihiro Hoshino | AFP | Getty Images

Jeff Williams, Apple's senior vice president of operations, told theFinancial Times that last month was the first time it was able to verify that none of the tantalum used in capacitors and resistors in its devices had comefrom mines in conflict regions. It is now urging "conflict-free" audits for gold, tin and tungsten suppliers by publishing a list of all its suppliers' smelters and their compliance with ethical sourcing guidelines every quarter. More from the Financial Times:

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Apple plants seeds for next big thing "We think it has the chance to make a difference," Mr Williams said."The smelters are a choke point where all this flows through. If we can get as many smelters verified [as possible] through this pressure, then we have a real chance of influencing the various activities on the ground." The electronics industry faces growing criticism from human-rightsorganisations and impending regulation from US financial authorities over itsextensive use of conflict minerals mined from sites controlled by violentmilitias in the Democratic Republic of Congo and nearby areas. "The fastest way for Apple to become conflict-free would be to channel our demand through a couple of verified smelters," Mr Williams said ahead of the publication of its annual "Supplier Responsibility" report.

"But quite honestly, if we did that, we could wave our conflict-freeflag but it would do nothing to affect the workers on the ground. And so whatwe are focused on is getting a critical mass of suppliers verified such that wecan truly influence the demand situation and change things." More than half of the world's tantalum flows through the electronicsindustry, Mr Williams said, making it easier to exert pressure through its supply chain to cut down the use of mines that are seen as "unacceptable from ahuman-rights standpoint". However, for tin, tungsten and gold, Apple and other technology companies are a smaller customer, and so it is using the glare of public scrutiny to encourage change. (Read more: Cramer: Apple's 'got something that could dazzle') The first publication of its quarterly report named 59 smelters that were already compliant, and 23 that were participating in the Conflict-Free Smelter Programme. This scheme is run by the Electronic Industry Citizenship Coalition, an independent organisation that counts Apple, Microsoft, IBM, HP, Sony and Dellamong its fee-paying members. The adherence to ethical guidelines of a further104 smelters, mainly processing gold and tin, was not known. Under the new Dodd Frank regulations, certain US companies are requiredto provide information to the Securities and Exchange Commission about their conflict mineral usage before a May deadline.