German investor morale was hit by the crisis in Crimea and fell to the lowest level since August, a survey found on Tuesday.

The Center for European Economic Research (ZEW) in Mannheim said its index for investor confidence in German economic outlook fell by 9.1 points to 46.6 points in March.

"In this month's survey, the Crimea crisis is weighing on experts' economic expectations for Germany," said ZEW President Clemens Fuest, adding that investors didn't consider Germany's economic upswing as at risk.

The survey, based on 241 analysts, found that the indicator reflecting current German economic situation improved by 1.3 points in March to 51.3 points.

Russian President Vladimir Putin signed a treaty on Tuesday to integrate Crimea and Sevastopol into Russia, following a referendum on Sunday which found that a large majority of Crimeans supported the reunification.

The European Union announced on Monday it would freeze assets of 21 Russian and Crimean officials and banned their visas. It also threatened to pose further economic sanctions on Russia.

German business worried that the sanctions would also hurt the German economy. Currently, there are some 6,000 German companies operating in Russia.

In 2013, German exported goods worth of 36 billion euros (about 50 billion U.S. dollars) to Russia, and imported goods worth about 40 billion euros.

According to German media reports, several German firms have suspended deliveries to their Russian factories in order to protect their investments from uncertainty. (1 euro = 1.39 U.S. dollars)