U.S. technology giant Apple said Friday it has filed a lawsuit in South Korea claiming Samsung Electronics infringed upon several patents.

Apple filed a lawsuit in April in the United States, claiming Samsung had copied its smart phones and tablet computers.

The South Korean company responded later that month with a lawsuit in Seoul, the U.S. and Germany, alleging patent infringements by Apple.

Despite the legal wrangling, the two firms have a close business relationship. Apple was Samsung's second-largest client last year, mainly purchasing semi-conductors.