More than 150 civil society organisations from around the globe are asking President Barack Obama to end the prosecution of Edward Snowden (Activists stage second national day of protest against NSA's domestic spying, 4 August).

Human rights, digital rights and media freedom campaigners from the UK to Uruguay and from the US to Uganda have joined together to call on the US administration to acknowledge Snowden as a whistleblower. All of us ask that he is protected and not persecuted.

Snowden's disclosures have triggered a much-needed public debate about mass surveillance online everywhere. Thanks to him, we have learned the extent to which our online lives are systematically monitored by governments, without transparency, accountability or safeguards from abuse.

Rather than address this gross abuse, the US government has chosen to shoot the messenger. It has revoked his passport and obstructed his search for asylum. European governments have been quick to help.

The knock-on effect will be to encourage others to follow by example. States that have even less regard for their citizens will justify attacks on those who put themselves at significant risk to expose wrongdoing and corruption or raise matters of serious public concern.

We urge President Obama to protect Snowden and other whistleblowers like him. We ask that the president initiate a full, public investigation into the legality of the National Security Agency's actions. Perhaps, then, David Cameron might consider doing the same over allegations concerning GCHQ.

Dr Agnes Callamard

Executive director, Article 19, on behalf of more than 150 global organisations