Grassroots protesters have been calling attention to rare metals that are mined with unethical practices or have been creating profits for warlords in the war-torn Democratic Republic of Congo, the New York Times reported.
In its annual report on its supply lines, Apple said that its sources used tantalum, a corrosion-resistant chemical element used in electronics, that was "conflict-free."
Apple said it had confirmed its report through third parties.
The company also said it was pressuring suppliers of gold, tungsten and tin to use conflict-free materials that go in to its products, which are mostly made overseas.
"For gold, tin and tungsten, Apple has had less success because it does not have as much financial leverage to pressure the smelters," the company said.
The Web site AppsGoneFree said Apple had increased audits of supplier factories 15 percent in 2013 compared to 2012, but that one supplier, Pegatron, had still been cited three times in the year for unethical work practices.
Apple has been pressured for several years to apply its own pressure on suppliers in China to improve working conditions. In Thursday's report, Apple said it was continuing to work with suppliers to comply with the company's workweek standards, which limit work to 60 hours per week.
Longer work weeks are allowed, but as an exception, not as a rule, Apple said.
"Workweeks exceeding 60 hours have been a persistent problem for the electronics industry, and reducing excessive overtime remains a priority for Apple. We limit workweeks to 60 hours, except in unusual circumstances. And all overtime must be absolutely voluntary," the report said.
Apple also said its free course on worker rights was attended by 280,000 supply line workers in 2013.
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