German authorities say they have searched a vessel suspected of carrying explosives used to blow up two Nord Stream pipelines last September.

The German federal prosecutor's office on Wednesday acknowledged having searched, mid-January, the ship suspected of transporting explosives to the site of the blasts in the Baltic Sea.

Authorities said they are evaluating seized objects.

German Defense Minister Boris Pistorius warned against any hasty conclusions on responsibility for the attacks. He said the move may have been a false flag operation staged to blame Ukraine.

German public broadcaster ARD and others reported on Tuesday a crew of six people of unknown nationality boarded a boat rented from a company owned by Ukrainians to carry out the sabotage.

The New York Times also on Tuesday reported new intelligence reviewed by US officials suggests that a pro-Ukrainian group carried out the attack on the Nord Stream pipelines last year.

The Ukrainian government denies involvement.