BERLIN - Germany's BKA federal police assumes explosions in the Nord Stream pipelines last week were "a targeted act of sabotage" and said it is probable that state actors were involved, the Spiegel weekly reported, citing a letter to industry representatives.

The BKA said in the letter that it did not yet have any findings about who was behind the sabotage but "against the background of the high complexity of the execution of the act and corresponding preparation, the action of state actors seems probable", Spiegel reported.

The BKA was not immediately available for comment.

A German government spokesman on Wednesday said all information available so far points to sabotage but declined to comment on whether state actors were responsible for it.

Europe is investigating what caused three pipelines in the Nord Stream network to burst in an act of suspected sabotage near Swedish and Danish waters.

Moscow sought to pin the blasts on the West, suggesting the United States stood to gain.

The BKA also warned of further sabotage acts against critical infrastructure in the wake of the explosions, in the letter seen by Spiegel on Wednesday.

There could be sabotage "in a quantitatively and, potentially, qualitatively increased form", it said.

Attacks could be directed against gas and power lines, as well as offshore liquefied natural gas terminals or wind turbines, among others, said the letter, according to Spiegel. REUTERS