Apple's popular iPhone 7 produced radiofrequency radiation above the legal limit in a new test, prompting the Federal Communications Commission (FCC) to investigate the issue.

The cellphone was set to operate at full power and was secured below a tub of clear liquid formulated to mimic human tissue during the test, which was conducted and paid for by The Chicago Tribune inside an accredited lab following federal guidelines. For 18 minutes, a tiny probe measured the radiofrequency radiation the liquid was absorbing from the iPhone 7.

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According to the Tribune, the test found radiofrequency radiation "over the legal safety limit and more than double what Apple reported to federal regulators from its own testing."

The newspaper tested three more brand new iPhone 7s at full power, and those also measured above the exposure limit. In total, 11 models from four different manufacturers were tested.

The FCC told the Tribune it would conduct its own testing over the next few months.

“We take seriously any claims on non-compliance with the RF (radiofrequency) exposure standards and will be obtaining and testing the subject phones for compliance with FCC rules,” agency spokesman Neil Grace said.

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As the Tribune notes, it's not clear whether prolonged exposure to radiofrequency radiation can increase the risk of cancers or cause other harm. With cellphones in wide use around the world, the issue is sure to receive increased scrutiny.

Two phone manufacturers, including Apple, disputed the Tribune's results, saying the lab that the newspaper used does not conduct tests the same way the tech giant does -- although the company did not specify exactly what was different or wrong about the Tribune's tests.

“All iPhone models, including iPhone 7, are fully certified by the FCC and in every other country where iPhone is sold,” Apple's statement to the Tribune said. “After careful review and subsequent validation of all iPhone models tested in the [Tribune] report, we confirmed we are in compliance and meet all applicable … exposure guidelines and limits.”

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The tests were conducted by RF Exposure Lab in San Marcos, Calif., which is recognized by the FCC as accredited to test for radiofrequency radiation from electronic devices.

Fox News has reached out to Apple with a request for comment on this story.