The main U.S. stock indexes slipped on Monday after military clashes between the United States and Iran drove up oil prices, stoking inflation fears after Fed Chair Kevin Warsh's hawkish remarks in his maiden Jackson Hole address the previous week. The losses could set the tone for September, typically a weak month for equities, and are likely to up the ante at the U.S. Federal Reserve's meeting next month. Traders see more than a 60 percent chance of a rate hike at the Fed's September meeting, according to CME's FedWatch, a sharp increase from 41.4 percent a week ago, after Warsh said policymakers may need to increase borrowing costs if inflation does not ease to the central bank's 2 percent target. "Absent a material downside surprise, the onus is now on Warsh to deliver a September hike. Otherwise, he risks undermining some of the credibility he gained on Friday," analysts at BofA Global Research said in a note. Warsh's comments, delivered on Friday at the Fed's Jackson Hole symposium in Wyoming, followed mixed data in recent weeks. A consumer inflation report this month showed price p