U.S. national security adviser Jake Sullivan said Tuesday night that he had spoken with his Danish counterpart about the leaks in the Nord Stream 1 and 2 gas pipelines, which he labeled "apparent sabotage."
"I spoke to my counterpart Jean-Charles Ellermann-Kingombe of Denmark about the apparent sabotage of Nord Stream pipelines," Sullivan tweeted. "The U.S. is supporting efforts to investigate and we will continue our work to safeguard Europe's energy security."
On Wednesday, White House press secretary Karine Jean-Pierre also said the leaks of the pipelines were the result of "apparent sabotage."
The pipelines, which run under the Baltic Sea, were not actually supplying gas to Europe at the time, although both did still contain gas.
"We have been in touch with our European partners there about the apparent sabotage of the pipelines," she told reporters. "We are supporting European efforts to investigate this. The investigation is still underway, and it could take some time."
Asked whether the United States would consider the leaks an attack on a NATO ally worthy of retaliation, Jean-Pierre said she wouldn't "get ahead of the investigation."
"We have to see who is behind this at this time," she said.
Some European leaders have gone further than U.S. officials have.
Denmark's prime minister said Tuesday that "it is the authorities' clear assessment that these are deliberate actions -- not accidents," although she added that "there is no information indicating who could be behind it," according to the Associated Press.
The Kremlin said accusations that Russia could be behind the leaks were "absurd," according to the Russian news agency Interfax.
"It is quite predictable and predictably ridiculous and absurd to make up such theories," Kremlin spokesman Dmitry Peskov told reporters Wednesday, noting "this gas costs a fortune but it is now siphoning off into the air."
Poland's prime minister called the development "an act of sabotage," and Sweden's acting prime minister said "it is probably a case of sabotage," the Associated Press reported.
Experts told ABC News that only one country -- Russia -- stood to benefit from the pipeline leaks, although officials have yet to offer evidence Russia was behind them.
"No one aside from Russia stands to gain from sabotaging these pipelines," said Ben Cahill, a senior fellow at the Center for Strategic and International Studies.
An act of sabotage on this scale fits neatly into Russian President Vladimir Putin's efforts "to sow confusion and panic in Europe and weaken European solidarity," Cahill said, but also carries tremendous risk for Moscow.
"If it is true that Russia is culpable, this is Putin cutting off his nose to spite his face," said Matthew Schmidt, director of the International Affairs program at the University of New Haven.
Also Wednesday, the United States announced $1.1 billion in new security assistance for Ukraine, including long-range missile systems, armored vehicles, radars and more.
ABC News' Matthew Seyler contributed to this report.
White House: Nord Stream gas pipeline leaks 'apparent sabotage' originally appeared on abcnews.go.com