STOCKHOLM, March 8. /TASS/. The North Atlantic Alliance is unaware who blew up the Nord Stream pipelines, NATO Secretary General Jens Stoltenberg said on Wednesday.

"What we do know is that there was an attack against the Nord Stream pipelines, but we have not been able to determine who was behind it," Stoltenberg said before a meeting with EU defense ministers in Stockholm.

He said the attack highlighted the need to protect critical undersea infrastructure.

Stoltenberg was commenting in the wake of recent reports in the New York Times and Die Zeit that a pro-Ukrainian group could be behind the sabotaging of the pipelines.