Euro zone sentiment improved for the sixth straight month in April as investors took heart from the European Central Bank's bond-buying program, raising the current situation component of the Sentix index to its highest in almost four years.

Sentix research group's index tracking morale among investors and analysts in the euro zone climbed to 20.0, its highest level since August 2007, from 18.6 the previous month. The reading was in line with the Reuters consensus forecast.

"Last month we were able to report the end of the recessionary phase for the euro area. In April, now the upswing signs for the euro zone have further compressed," Sentix said in a statement on Tuesday.

Investors in the euro zone were at their most upbeat about the current situation since July 2011, suggesting concerns about a possible Greek exit from the euro zone had no significant impact on sentiment.

The euro fell 11 percent against the dollar in the first quarter, driven by the ECB unleashing a 1 trillion euro bond buying program last month to boost economies in the 19-country bloc.

However, the index tracking Germany fell in April to 31.4 after hitting an all-time high the previous month. Sentix said the sub-components still indicated that Germany's domesticeconomy was in a robust state.

The survey of 953 investors was conducted between April 2 and April 4.