WASHINGTON, Oct 4 (Reuters) - The National Highway Traffic Safety Administration (NHTSA) has rejected a 2019 petition to open a formal investigation into Tesla (TSLA.O) vehicle fires, according to a federal filing on Monday. The agency opened a formal review in October 2019 of the petition filed by the offices of California lawyer Edward C. Chen on behalf of Tesla owners over non-crash fire concerns including reports of three fires in China. The NHTSA said in 2019 it was reviewing whether Tesla should have recalled 2,000 of its electric cars that year instead of issuing a software upgrade to fix a potential defect that could result in battery fires. The petition alleged Tesla was "using over-the-air software updates to mask and cover up a potentially widespread and dangerous issue with the batteries in their vehicles." Tesla’s investigation of the non-crash fires in China did not identify a root cause or positively link the incidents to any design or manufacturing defect conditions," NHTSA"s denial said, adding: "The available data indicate that non-crash battery fires in Tesla vehicles are rare events." Tesla did not immediately respond to a request for comment. The NHTSA added "no fires related to the subject condition have been observed globally since three fires in China and Hong Kong over a 48-day period from late-March to mid-May 2019." It added "there have been no fires in the United States related" to the issue.