WASHINGTON — U.S. consumer prices increased slightly in July, potentially weakening the argument for an interest rate increase from the Federal Reserve next month. The Consumer Price Index edged up 0.1 percent last month after dropping 0.4 percent in June, which was the first decline in six years, the Labor Department's Bureau of Labor Statistics said on Wednesday. In the 12 months through July, the CPI advanced 3.4 percent after rising 3.5 percent in June. Excluding the volatile food and energy components, the CPI gained 0.2 percent last month after being unchanged in June. The so-called core CPI increased 2.5 percent in the 12 months through July after climbing 2.6 percent in June. Economists polled by Reuters had forecast the CPI rebounding 0.1 percent and core inflation rising 0.2 percent over the month. The U.S. central bank tracks the Personal Consumption Expenditures price indexes for its 2 percent inflation target. The CPI report followed news last week of surprise job losses last month. Prior to the CPI report, financial markets saw a roughly 46 percent chance of a rate hike a