"These investigations have not yet been concluded. At this point, it is not possible to say when they will be concluded," the letter said.
The UN Security Council is meeting on Tuesday to discuss "sabotage" after Russia asked for an independent inquiry into the September attacks on the pipelines that spewed gas into the Baltic Sea.
According to diplomats, a vote on a Russian draft resolution calling for an international investigation is not initially planned.
However, one diplomat told the DPA news agency that a push by Russia for a vote is expected in the coming days.
Sweden and Denmark, in whose exclusive economic zones the explosions occurred, have concluded the pipelines carrying natural gas from Russia to Germany were blown up deliberately but have not said who might be responsible.
The letter said Russian authorities had been informed about the investigations and reiterated that the damage was a deliberate act of sabotage.
In Germany, the federal prosecutor has launched a criminal investigation to establish if a crime of sabotage under section 88 of the criminal code was committed, the letter said.
The Kremlin has accused the United States of carrying out an attack on the pipelines.
Russian politicians have for days been working off uncorroborated claims by veteran US journalist Seymour Hersh, citing a single anonymous source.Â
He wrote that US navy divers were responsible for the explosions but the White House dismissed the report as a fabrication.
Russia's draft resolution at the UN mentions that the attack took place after "repeated threats" from the US.
Germany was not initially scheduled to attend Tuesday's meeting in New York.
with DPA
