Multiple leaks were discovered on the Nord Stream 1 and 2 pipelines connecting Russia to Germany, further raising political tensions already sky high since the Kremlin invaded Ukraine in February. All four leaks were located near Danish island Bornholm.

Russian President Vladimir Putin has said the leaks were an act of “international terrorism” that would benefit the United States, Poland and Ukraine.

Both Moscow and Washington have denied responsibility for the leaks, which were discovered in late September. Germany, Sweden and Denmark have formed a joint investigation unit to probe the apparent sabotage.

“The heads of the diplomatic missions of Germany, Denmark and Sweden in Moscow have been summoned to the Russian foreign ministry in recent days,” the Russian ministry said in a statement.

The ministry said it “expressed bewilderment” over the lack of an official response to a request from Russia’s Prime Minister Mikhail Mishustin to involve Russian energy giant Gazprom and “representatives of the competent departments” from Russia in the investigation conducted by Berlin, Copenhagen and Stockholm.

The envoys were told that if Russian experts are not involved “Moscow will proceed from the fact that the named countries have something to hide or they are covering for the perpetrators of these terrorist acts”, the ministry said.

It added that Russia will not recognise any “pseudo-results” of an investigation without its experts.

A spokesman for the German federal prosecutor’s office said earlier this week that it was investigating “against persons unknown” on suspicion of “intentionally causing an explosive blast” and “sabotage” linked to the leaks.

Germany’s federal prosecutor’s office typically only opens investigations into cases involving national security such as terror attacks.