German prosecutors are investigating two men suspected of planning terrorist attacks using model aeroplanes after authorities in Germany and Belgium conducted a series of searches.

No one was arrested in today's raids, which were carried out to gather "evidence for possible attack plans and preparations" and information on terrorist financing, federal prosecutors said in a statement.

Prosecutors said the investigation involves possible charges of "preparation of a serious, state-threatening act of violence," but not membership of or supporting any terrorist organisation.

In all, nine properties were searched in the Stuttgart and Munich areas of southern Germany, in eastern Germany's Saxony state and in Belgium.

The two men of Tunisian origin are suspected of "procuring information and objects to commit Islamic extremist explosive attacks with remote-controlled model aeroplanes," prosecutors added. They gave no further information on the two men and didn't identify them.

The apartments of four acquaintances of the men, suspected of financing Islamic extremism, were searched in Germany. The investigation also targets a further acquaintance suspected of money laundering. None of the suspects were identified.

Last November a US man, Rezwan Ferdaus, was sentenced to 17 years in prison over a plot to fly remote-controlled model planes packed with explosives into the Pentagon and US Capitol.

Germany has seen only one successful attack by an Islamic radical - the fatal shooting of two US airmen at Frankfurt airport in 2011 by a Kosovo native who grew up in Germany and became radicalised on his own by watching jihadist propaganda on the Internet.

However, there have been several attempted attacks in the country, which is a major contributor to international forces in Afghanistan.