Action is under way in the Bundestag to commission a parliamentary investigation into US intelligence service spying and a German politician met Snowden in Moscow on Thursday to discuss the matter.
Hans-Christian Ströbele, the veteran Green party candidate for Berlin's Kreuzberg district, reported that the US whistleblower was prepared in principle to assist a parliamentary inquiry.
But Ströbele warned of the legal complications that would come with Snowden leaving Russia, where he has been granted asylum after leaking documents on mass NSA surveillance. Witnesses to parliamentary enquiries are usually given the financial support and legal protection required for them to travel to Germany.
During the meeting, Snowden handed Ströbele a letter addressed to the German chancellor, Angela Merkel, which will be read out publicly on Friday afternoon.
The latest developments will encourage those who hope Germany may eventually grant political asylum to Snowden. In June, his application for asylum there was rejected by the foreign ministry because, legally, he had to apply for asylum in person and on German soil. If Snowden was brought to Germany as a witness, he could meet these requirements.
Activists are said to be considering other means of getting Snowden to Germany. Under paragraph 22 of the German residence law, Snowden could be granted a residence permit "if the interior ministry declares it to be in Germany's political interest". After reports of Merkel's mobile phone being hacked by the NSA, such conditions could be said to apply.
Some German politicians and newspaper columnists have backed calls for Snowden to be invited as a witness. The justice minister, Sabine Leuheusser-Schnarrenberger, told the Passauer Neue Presse newspaper: "If the allegations build up and lead to an investigation, one could think about calling in Snowden as a witness."
Thomas Oppermann, of the Social Democrats, said: "Snowden's claims appear to be credible, while the US government has blatantly lied to us on this matter. That's why Snowden could be an important witness, also in clearing up the surveillance of the chancellor's mobile."
In Süddeutsche Zeitung, the columnist Heribert Prantl wrote: "Granting asylum to Snowden could be a way of restoring Germany's damaged sovereignty."
The Bundestag will hold a special session to discuss NSA spying on 18 November. The Green party and the leftwing Die Linke have been leading calls for that session to result in a parliamentary investigation. Latest reports indicate that the Social Democratic party will support such a move, which would mean it would most likely go ahead.