Polish officials involved were slow to provide information and withheld key evidence about the movement of the saboteurs on Polish soil, The Wall Street Journal reported, citing investigators on January 8.

Investigators now hope the new government in Warsaw, which took office last month, will help shed light on the attack.

European investigators have long believed the attack was launched from Ukraine via Poland. But they say a lack of full cooperation from Warsaw has made it difficult to determine whether the Polish government was aware of the attack at the time.

Several senior European officials say they are considering reaching out to the office of new Polish Prime Minister Donald Tusk to help investigate the biggest act of sabotage in Europe since World War II.

The Nord Stream pipeline connecting Russia to Germany under the Baltic Sea exploded in September 2020. This increased pressure on Germany and others to become independent of Russian fuel supplies.

Any suggestion that Poland, a NATO member, might conceal information about an attack on an ally could undermine confidence in an alliance facing one of its biggest challenges since its founding.

For Moscow, any Polish action that hints at involvement in sabotage could be seen as an act of aggression by NATO.

It should be made clear that investigators have not produced evidence of Polish government involvement in the explosions and suggest that even if some Polish officials were involved, the political leadership may not have been aware of it.

However, investigators say efforts by Polish officials to obstruct the investigation have increasingly raised doubts about Warsaw's role and motives.

Ukraine has denied any involvement. Russia, meanwhile, has blamed the US for the attack, which the US denies.

After taking office, Prime Minister Tusk fired the heads of all intelligence agencies, including those involved in the Nord Stream pipeline investigation.

Polish prosecutors overseeing the domestic investigation said they were cooperating with other countries, but had not found any evidence of Polish involvement. Poland’s border guard and internal security agency declined to comment.