Sarah Harrison, the British journalist and WikiLeaks staffer who has been working with Edward Snowden since his arrival in Moscow, has left Russia and joined the growing band of net activists stranded in Berlin.

A statement released on the WikiLeaks website, attributed to Harrison, states that she arrived in Germany on Saturday and has been advised by her lawyers that it is "not safe to return home" to the UK.

Harrison joins a growing group of journalists and activists who were involved in the publication of Snowden's files and are now living in the German capital "in effective exile", including Laura Poitras and Jacob Applebaum.

The statement, which is also quoted on Spiegel website, accused the US and UK governments of using "aggressive tactics" against journalists who have reported on unethical surveillance practices.

"It should be fanciful to suggest that national security journalism which has the purpose of producing honest government or enforcing basic privacy rights should be called 'terrorism', but that is how the UK is choosing to interpret this law."

Harrison has appeared in many of the photographs of Snowden that have emerged from Russia. Last Thursday, she was present at the meeting between the NSA whistleblower and the German Green politician Hans-Christian Ströbele in Moscow.

The statement does not clarify why Harrison, 31, left Moscow, but says: "Edward Snowden is safe and protected until his asylum visa is due to be renewed in nine months time", and that "there is still much work to be done".

Harrison, a graduate of City University's journalism programme, first started working with WikiLeaks before the Afghan war documents leak and played a key role during the publication of the embassy cables and in Julian Assange's fight against extradition to Sweden. She accompanied Snowden on the flight from Hong Kong to Moscow on 23 June.

• This article was amended on 6 November 2013. The original picture showed Edward Snowden with Jesselyn Raddack, not Sarah Harrison. This has been corrected