(Reuters) - Apple Inc sent an invite to reporters on Thursday for an event at its Cupertino, California headquarters on March 21, possibly signaling the unveiling of a new iPhone. The world's best-known technology company often reveals new products at such events. It is expected to update its flagship iPhone and iPad products soon. Apple shares have risen in the past two weeks as Wall Street bets the company will launch a less expensive iPhone this month to boost sales in developing countries like China. With U.S. consumers upgrading their smartphones less often, manufacturers have been relying on China for growth. (Reporting by Julia Love; Editing by Bill Rigby)