The White House on Wednesday dismissed a blog post by a US investigative journalist alleging the United States was behind explosions of the Nord Stream gas pipelines as “utterly false and complete fiction”.

Reuters has not corroborated the report, published by US investigative journalist Seymour Hersh, which said an attack was carried out last September at the direction of US President Joe Biden.

“This is utterly false and complete fiction,” said Adrienne Watson, a spokesperson for the White House National Security Council. Spokespeople for the CIA and State Department said the same.

The pipelines are multibillion-dollar infrastructure projects designed to carry Russian gas to Germany under the Baltic Sea.

Sweden and Denmark, in whose exclusive economic zones the blasts occurred, have both concluded the pipelines were blown up deliberately, but have not said who might be responsible.

The United States and Nato have called the incident “an act of sabotage”.

Moscow has blamed the West for the unexplained explosions that caused the ruptures. Neither side has provided evidence.

On Wednesday, Russia’s foreign ministry said the United States had questions to answer over its role in explosions on the pipelines.

“The White House must now comment on all these facts,” Foreign Ministry spokeswoman Maria Zakharova said in a post on her Telegram page where she summarised Hersh’s main claims.

Construction of Nord Stream 2, designed to double the volume of gas that Russia could send directly to Germany under the sea, was completed in September 2021, but was never put into operation after Berlin shelved certification just days before Moscow sent its troops into Ukraine last February.

Hersh is a former New York Times and New Yorker reporter who won numerous awards for his investigative journalism, including about the Vietnam War and the 2004 Abu Ghraib scandal following the US invasion of Iraq.

More recently, he ignited controversy with a report disputing the Obama administration’s version of the 2011 killing of al Qaeda founder Osama bin Laden in a US special forces operation, and another accusing Syrian rebels of staging an August 2013 sarin nerve agent attack on a Damascus suburb that killed hundreds of civilians.