DUESSELDORF, Germany (Reuters) - German authorities on Wednesday searched 15 properties across the country in connection with an investigation into protests by the Last Generation climate activist group, police said.

Prosecutors in the city of Munich are investigating seven suspects aged between 22 and 38 on suspicion of forming or supporting a criminal organisation, police said in a statement. No arrests have been made.

The suspects are believed to have been raising funds to finance further crimes on behalf of Last Generation, collecting at least 1.4 million euros ($1.54 million) in donations, according to police.

Two of the defendants are suspected of sabotaging the Trieste-Ingolstadt oil pipeline - considered critical infrastructure and therefore subject to special protection - in April last year.

The searches took place in Hesse, Hamburg, Saxony-Anhalt, Saxony, Bavaria, Berlin and Schleswig-Holstein.

Last Generation activists have been causing large-scale disruption across Germany in recent months by glueing themselves to roads and blocking rush-hour traffic.

(Reporting by Anneli Palmen; Writing by Friederike Heine; Editing by Robert Birsel)