Euro zone investor sentiment improved this month for the first time since March thanks to the European Central Bank's plans to rescue the common currency, Sentix research group said on Monday. Sentix said its monthly index tracking investor sentiment in the 17-nation currency bloc climbed to -23.2 in September, up from -30.3 in August, and well above a Reuters consensus forecast for a dip to -30.7. "The main reason for the general improvement in sentiment could well be ECB President Mario Draghi's continued assertive manner and his institution's intention, which is now concrete, to start buying crisis-stricken countries' bonds again soon if they fulfil certain conditions," Sentix said in a statement. Last week the ECB agreed to launch a new and potentially unlimited bond-buying programme to lower struggling euro zone countries' borrowing costs and draw a line under the debt crisis. A sub-index measuring expectations rose for a second straight month to -10.8 from -23.3 in August. "ECB President Mario Draghi's bazooka with conditions has clearly beguiled investors because the expectations index jumped up in September in all of the countries and regions surveyed by Sentix," the group said. Sentix added that institutional investors were becoming increasingly optimistic in all countries and regions while private investors remained more cautious. The Sentix sub-index tracking current conditions rose slightly, climbing to -34.8 from -37.0 the previous month.