Wall Street's key indices closed lower after Federal Reserve Chair Kevin Warsh reiterated the central bank's focus on fighting inflation, increasing prospects for a rate hike.Without confidence that inflation is heading clearly and with sufficient speed to the Fed's 2% goal, the central bank would have "more work to do," Mr Warsh said in his first Jackson Hole speech to fellow central bankers.That saw early gains in US equities fade, while European markets had already closed and finished the session with handy gains.S&P 500: -0.25%Dow: -0.02%Nasdaq: -0.5%Eurostoxx 600: +0.5%ASX 200 futures trading closed on Saturday morning (AEST) pointing to a 0.4% decline…