By Natasha Bertrand and Katie Bo Lillis, CNN
(CNN) - The US warned several European allies over the summer, including Germany, that the Nord Stream 1 and 2 pipelines could face threats and even be attacked, according to two people familiar with the intelligence and the warnings.
The warnings were based on US intelligence assessments, but they were vague, the people said -- it was not clear from the warnings who might be responsible for any attacks on the pipelines or when they might occur.
The CIA declined to comment.
Der Spiegel was the first to report on the intelligence warnings.
On Monday, leaks were discovered in the pipelines, prompting investigations by European authorities that determined powerful underwater explosions had occurred just before the pipelines burst in several places.
US national security adviser Jake Sullivan and NATO Secretary General Jens Stoltenberg have now both characterized the incident as an act of sabotage, but European officials have not yet publicly identified a culprit.
US, European and Ukrainian officials have been warning for months, however, that critical infrastructure -- not only in Ukraine but also in the US and Europe -- could be targeted by Russia as part of its war on Ukraine.
The Kremlin on Wednesday called insinuations that it would sabotage the pipeline "predictably stupid and absurd."
"It's pretty predictable and predictably stupid to express such versions," Kremlin spokesperson Dmitry Peskov told reporters.
"This is a big problem for us, since both pipelines are filled with gas, and this gas is very expensive," he added. He said Moscow still does "not understand what happened there ... there are a lot of questions."
Neither of the pipelines were pumping gas to Europe when the incident occurred. Russia shut off gas flows to Europe through Nord Stream 1 weeks ago, saying it had to do technical work on the pipeline but also as retaliation for western sanctions over its invasion of Ukraine. The Nord Stream 2 pipeline, meanwhile, was not yet completed before Germany killed the project in response to Russia's invasion.
Still, the Nord Stream 1 pipeline provided Russia with significant leverage over Europe for years, as CNN has previously reported. European countries have been shoring up energy supplies to prepare for winter amid Russia's weaponization of energy resources, but western officials remain concerned about potential shortages if winter is particularly harsh.
Any hopes that Russia could start pumping gas through Nord Stream 1 next year, however, have largely been dashed now that the pipeline has been so badly damaged, the sources told CNN.
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