Curiouser and Curiouser.

Who would want to remind the European countries in NATO of their vulnerabilities? Who, who?

“It’s hard to assess, does anybody benefit?” Finland’s president, Sauli Niinistö, told the news outlet Helsingin Sanomat. “That is why this is a mystery so far.”

Some European and American officials cautioned on Wednesday that it would be premature to conclude that Russia had been behind the apparent attacks. President Vladimir V. Putin likes to show he has his finger on the gas valve, they noted, but wielding that power could mean keeping the pipelines in good working order.

Many Western officials and analysts said sabotage would fit neatly into Mr. Putin’s broader Russian strategy of waging war on multiple fronts, military and economic. The sabotage drives home to a jittery Europe how vulnerable its infrastructure is.

“This is classic hybrid warfare,” said Marie-Agnes Strack-Zimmermann, head of the defense committee in Germany’s Parliament, who stressed that for now she had no evidence Russia was behind the attack but believed it was the most “plausible” culprit.

— Katrin Bennhold and David E. Sanger

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The C.I.A. had warned European governments of potential attacks on pipelines.

The warning was not specific, the officials said, and they declined to say whether Russia was identified as a possible attacker.

By DAVID E. SANGER and JULIAN E. BARNES