Mumbai, Sept. 1 -- COMEX copper futures extended gains in early Asia on Tuesday and are holding around record high levels as dollar gave up much of gains and edged sharply lower yesterday. Dollar index steadies around 99.5 on Tuesday after declining in the previous session, as investors continued to assess prospects for Federal Reserve interest rate hikes following hawkish comments from Chair Kevin Warsh and rising oil prices. Meanwhile, data showed that copper output in top producer Chile fell 9.4% in July from a year earlier, highlighting tightening conditions in global markets. US equities however ended the day in negative, limiting gains in the red metal that is currently quoting at $6.72 per pound, up half a percent on the day. The Dow...