part 2

Since the explosions along the pipelines in September, there has been rampant speculation about what transpired on the sea floor near the Danish island of Bornholm.

Poland and Ukraine immediately accused Russia of planting the explosives, but they offered no evidence.

Russia, in turn, accused Britain of carrying out the operation — also without evidence. Russia and Britain have denied any involvement in the explosions.

Last month, the investigative journalist Seymour Hersh published an article on the newsletter platform Substack concluding that the United States carried out the operation at the direction of Mr. Biden. In making his case, Mr. Hersh cited the president’s preinvasion threat to “bring an end” to Nord Stream 2, and similar statements by other senior U.S. officials.

U.S. officials say Mr. Biden and his top aides did not authorize a mission to destroy the Nord Stream pipelines, and they say there was no U.S. involvement.

Any findings that put blame on Kyiv or Ukrainian proxies could prompt a backlash in Europe and make it harder for the West to maintain a united front in support of Ukraine.

U.S. officials and intelligence agencies acknowledge that they have limited visibility into Ukrainian decision-making.

Despite Ukraine’s deep dependence on the United States for military, intelligence and diplomatic support, Ukrainian officials are not always transparent with their American counterparts about their military operations, especially those against Russian targets behind enemy lines. Those operations have frustrated U.S. officials, who believe that they have not measurably improved Ukraine’s position on the battlefield, but have risked alienating European allies and widening the war.

The operations that have unnerved the United States included a strike in early August on Russia’s Saki Air Base on the western coast of Crimea, a truck bombing in October that destroyed part of the Kerch Strait Bridge, which links Russia to Crimea, and drone strikes in December aimed at Russian military bases in Ryazan and Engels, about 300 miles beyond the Ukrainian border.

But there have been other acts of sabotage and violence of more ambiguous provenance that U.S. intelligence agencies have had a harder time attributing to Ukrainian security services.

One of those was a car bomb near Moscow in August that killed Daria Dugina, the daughter of a prominent Russian nationalist.

Kyiv denied any involvement but U.S. intelligence agencies eventually came to believe that the killing was authorized by what officials called “elements” of the Ukrainian government. In response to the finding, the Biden administration privately rebuked the Ukrainians and warned them against taking similar actions.

The explosions that ruptured the Nord Stream pipelines took place five weeks after Ms. Dugina’s killing. After the Nord Stream operation, there was hushed speculation — and worry — in Washington that parts of the Ukrainian government might have been involved in that operation as well.

The new intelligence provided no evidence so far of the Ukrainian government’s complicity in the attack on the pipelines, and U.S. officials say the Biden administration’s level of trust in Mr. Zelensky and his senior national security team has been steadily increasing.

Days after the explosion, Denmark, Sweden and Germany began their own separate investigations into the Nord Stream operation.

Intelligence and law enforcement agencies on both sides of the Atlantic have had difficulty obtaining concrete evidence about what happened on the sea floor in the hours, days and weeks before the explosions.

The pipelines themselves were not closely monitored, by either commercial or government sensors. Moreover, finding the vessel or vessels involved has been complicated by the fact that the explosions took place in a heavily trafficked area.

That said, investigators have many leads to pursue.

According to a European lawmaker briefed late last year by his country’s main foreign intelligence service, investigators have been gathering information about an estimated 45 “ghost ships” whose location transponders were not on or were not working when they passed through the area, possibly to cloak their movements.

The lawmaker was also told that more than 1,000 pounds of “military grade” explosives were used by the perpetrators.

Spokespeople for the Danish government had no immediate comment. Spokespeople for the German government declined to comment.

Mats Ljungqvist, a senior prosecutor leading Sweden’s investigation, told The New York Times late last month that his country’s hunt for the perpetrators was continuing.

“It’s my job to find those who blew up Nord Stream. To help me, I have our country’s Security Service,” Mr. Ljungqvist said. “Do I think it was Russia that blew up Nord Stream? I never thought so. It’s not logical. But as in the case of a murder, you have to be open to all possibilities.”

Reporting was contributed by Rebecca R. Ruiz, Erika Solomon, Melissa Eddy, Michael Schwirtz and Andrew E. Kramer.

Julian E. Barnes is a national security reporter based in Washington, covering the intelligence agencies. Before joining The Times in 2018, he wrote about security matters for The Wall Street Journal. @julianbarnes • Facebook

Adam Goldman reports on the F.B.I. and national security from Washington, D.C., and is a two-time Pulitzer Prize winner. He is the coauthor of “Enemies Within: Inside the NYPD's Secret Spying Unit and bin Laden's Final Plot Against America.”
@adamgoldmanNYT