South Korean anti-trust regulators carried out a raid on Google's offices in Seoul, technology news site CNET reported.
CNET said it was not immediately clear why Google's offices were targeted by the Korean Fair Trade Commission (KFTC).
Contacted by AFP, a Google spokeswoman said the Internet search giant "will work with the KFTC to address any questions they may have about our business."
In April, South Korea's top two Internet companies filed complaints with the KFTC accusing Google of stifling competition in the local mobile phone search market.
Daum and NHN Corp said Google exploited its position as developer of the Android mobile operating system to have its search function preloaded on local smartphones.
They said this limited access by local search engines to smartphones using Android.
"We neither confirm nor deny the report," a KFTC spokesman told AFP.
"We are afraid that divulging details of the probe may hamper our investigations and cause damage in the businesses of the company under investigation."
Google denied on Tuesday that it requires handset manufacturers to use Google search.
"Android is an open platform, and carrier and OEM (original equipment manufacturer) partners are free to decide which applications and services to include on their Android phones," the spokeswoman said.
"We do not require carriers or manufacturers to include Google Search or Google applications on Android-powered devices," she said.
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