The U.S. International Trade Commission said on Friday it has agreed to investigate Apple Inc's patent infringement complaint against Nokia Oyj, as the legal battle between the two technology heavyweights continues to play out.

The companies have been locked in a legal tussle since last October, when Nokia sued Apple and said the iPhone maker was using its patented technologies without paying for them.

Apple countersued Nokia, and both companies have turned to the ITC, filing complaints with the trade body.

Apple is asking the ITC to block Nokia from selling some mobile devices in the U.S. Apple contends the products infringe upon nine of its patents.

The case will be assigned to one of the ITC's six administrative law judges, who will hold an hearing on the evidence. The trade body will set a target date for completing its probe with 45 days after beginning the investigation.

The ITC agreed last month to investigate Nokia's complaint against Apple. Nokia alleges Apple infringed seven of its patents.

The legal dispute between Nokia and Apple potentially involves hundreds of millions of dollars in annual royalties.

Nokia is the world's largest mobile phone maker but has had trouble in the fast-growing smartphone market. Apple entered the smartphone market in 2007 but has seen huge success with the iPhone.

(Reporting by Gabriel Madway, editing by Gerald E. McCormick)