SK Hynix Inc. has opened an investigation into the use of its chips in the latest phone from Huawei Technologies Co., after a teardown of the device revealed its memory and flash storage inside.

Shenzhen-based Huawei’s Mate 60 Pro uses Hynix’s LPDDR5 and NAND flash memory, said TechInsights, who conducted the teardown of the device for Bloomberg News. The handset’s components are almost entirely provided by Chinese suppliers and Hynix’s hardware is an isolated example of materials sourced from overseas, according to TechInsights.

Icheon-based Hynix “no longer does business with Huawei since the introduction of the US restrictions against the company and, with regard to the issue, we started an investigation to find out more details,” a company spokeswoman said in a statement to Bloomberg News on Thursday. “SK Hynix is strictly abiding by the US government’s export restrictions.”

Read more: US Seeks Details on Made-in-China Huawei Chip as Debate Grows

Hynix shares in Seoul erased gains on the day after the statement. A Huawei representative did not immediately respond to a request for comment.

It’s unclear how Huawei may have procured the memory chips from Hynix, which makes most of its semiconductors at plants in China. One possibility is that Huawei may be tapping a stockpile of components it accumulated as far back as 2020 before the full set of US trade curbs had been imposed on it. International suppliers of advanced technology have been prohibited from supplying Huawei over the past three years by US trade curbs, implemented on fears of the hardware being used to aid China’s military.

--With assistance from Sohee Kim and Gao Yuan.

(Updates with shares reaction and additional details from teardown)