Edward Snowden has hinted at his willingness to travel to Germany to speak to a parliamentary inquiry about the US National Security Agency surveillance.

In a letter that has been passed on to the German chancellor, Angela Merkel, the whistleblower says he hopes he will "be able to cooperate in the responsible finding of fact regarding reports in the media, particularly in regard to the truth and authenticity with the law".

The content of the letter was revealed in a press conference by Green politician Hans-Christian Ströbele in Berlin on Friday. Ströbele had met Snowden in Moscow on Thursday in order to discuss the possibility of the former NSA employee being invited to Germany as a witness in a parliamentary inquiry.

Ströbele, a veteran parliamentarian who represents Berlin's Kreuzberg district, reported that Snowden "could imagine coming to Germany, as long it was guaranteed that he could stay in Germany or a comparable country thereafter and stay safe there". He also noted the whistleblower's reservations about speaking to German representatives on Russian soil.

Snowden has had his US passport revoked and is thus officially stateless – his asylum in Russia is temporary.

Witnesses to parliamentary inquiries are usually given the financial support and legal protection required for them to travel to Germany. Some legal experts claim a guarantee of safe conduct from German authorities would also render Snowden immune to US rendition requests.

Merkel's interior minister had earlier anticipated Snowden's letter by issuing a statement indicating the government would be prepared to meet Snowden. Hans-Peter Friedrich said that "we will find ways to enable a conversation if Mr Snowden is prepared to speak to German authorities". The interior ministry had previously stated that a meeting with the US whistleblower was out of the question.

In the letter, which is addressed to "To whom it may concern" and doesn't mention Germany explicitly, Snowden says that the US government "continues to treat dissent as defection, and seeks to criminalize political speech with felony charges that provide no defense". He adds: "Speaking the truth is not a crime".

Ströbele said Snowden had told him that he would prefer to speak in front of the US Congress rather than the German Bundestag if he had the choice.

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.

Germany is subject to an extradition treaty between the EU and the US which came into effect on 1 February 2010. But a legal report commissioned by Die Linke party and seen by the Guardian claims that Germany could have grounds for refusing an extradition request if the prosecution against Snowden could be shown to be "of political character".

Legal opinion is, however, divided on the subject. Klaus Dienelt, a migration lawyer, told the Guardian: Snowden's case is politically relevant, but that doesn't mean that the prosecution against him is politically motivated". Given that treason was accepted as a crime in both Germany and America, Dienelt said he thought it was "unlikely" Germany could refuse an extradition request.

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 Leutheusser-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.