FRANKFURT, Aug 24 - The European Central Bank on Friday dismissed market rumours that next week's euro zone M3 money supply data will show a strong number, stressing that the figure has not been calculated yet. "The M3 data has not yet been compiled so any number being discussed in the market is purely speculative," an ECB spokesman said. The ECB is due to release July figures at 0800 GMT on Tuesday and market talk that the data will show a strong rise triggered a sell-off of Euribor future contracts. In June M3 grew 6.1 percent year-on-year and another high reading could be seen as lengthening the odds for an interest rate cut at the ECB's next meeting on August 30.