Samsung Electronics Co said on Thursday, Sept 20, it plans to add Apple's iPhone 5, which goes on sale this week, to its existing patent lawsuits against the U.S. smartphone rival.

The fresh legal step by the South Korean firm comes as Apple booked orders for over two million iPhone 5 models in the first 24 hours and the model hits store shelves on Friday.

"Samsung anticipates that it will file, in the near future, a motion to amend its infringement contentions to add the iPhone 5 as an accused product," it said in a U.S. court filing, according to Reuters.