South Korean antitrust authorities have raided the Seoul offices of Google Inc. as part of an investigation into allegations of unfair trade in the nation's mobile-search-engine industry.

The Korean Fair Trade Commission was expected to return Wednesday in a follow-up raid, Reuters reported.

The initial raid on Tuesday followed accusations in April by Korean portal operators Daum Communications Corp. and NHN Corp. that the world's largest search engine is limiting their access to smartphones using the Android operating system.

NHN accused Google, which owns Android, of preventing South Korean phone manufacturers from including Web search applications made by other companies by delaying Android certification for handset makers that do so, Bloomberg said.

In a statement Tuesday Google said it does not require manufacturers of mobile phones that use its Android software to include Google search or other Google applications on the devices. It also said it would cooperate with the Korean Fair Trade Commission in its investigation.

We will work with the KFTC to address any questions they may have about our business, Google said. Android is an open platform, and carrier and OEM partners are free to decide which applications and services to include on their Android phones. We do not require carriers or manufacturers to include Google Search or Google applications on Android-powered devices.