A year after the attacks on the offices of Charlie Hebdo, and as the French satirical magazine’s latest issue draws fire from the Vatican, free speech organisations around the world have come together to proclaim the importance of protecting dissenting voices – and to attack those governments that have increased surveillance in the wake of the murders.

Twelve people were killed by gunmen in Charlie Hebdo’s Paris offices a year ago on Thursday. Marking the atrocity, a statement led by writers’ organisation PEN International and signed by more than 70 PEN centres and freedom of expression groups underlines their “commitment to the defense of the right to freedom of expression, even when that right is being used to express views that some may consider offensive”.

Palestinian poet Ashraf Fayadh, who was sentenced to death in November 2015 after being accused of renouncing Islam. Photograph: Uncredited/AP

The year following the attacks on 7 January 2015 has seen “intense repression” of artists and writers around the world, says PEN International, “despite the turnout of world leaders on the streets of Paris in an unprecedented display of solidarity with free expression following the Charlie Hebdo murders”. They cite the possible 43-year sentence for the cartoonist Zunar in Malaysia for alleged sedition, the 12-year sentence for cartoonist Atena Farghadani in Iran over a political cartoon, and the sentencing to death of the Palestinian poet Ashraf Fayadh in Saudi Arabia.

In the letter, PEN says the most far-reaching threats to free speech over the past year actually come from governments “ostensibly motivated by security concerns”, pointing to the statement issued by EU interior ministers after the attacks asking internet service providers to remove content that aimed to “incite hatred and terror”. The statement also condemns France’s new surveillance laws.

“This kind of governmental response is chilling because a particularly insidious threat to our right to free expression is self-censorship. In order to fully exercise the right to freedom of expression, individuals must be able to communicate without fear of intrusion by the state,” they write.

“Under international law, the right to freedom of expression also protects speech that some may find shocking, offensive or disturbing. Importantly, the right to freedom of expression means that those who feel offended also have the right to challenge others through free debate and open discussion, or through peaceful protest.”

The 78 free-speech organisations call on all governments to protect freedom of expression, “especially for journalists, writers, artists and human rights defenders to publish, write and speak freely”, and to repeal legislation that “restricts the right to legitimate freedom of expression, especially vague and overbroad national security, sedition, obscenity, blasphemy and criminal defamation laws, and other legislation used to imprison, harass and silence critical voices, including on social media and online”.

The Charlie Hebdo anniversary edition represents God as a terrorist bearing a gun. Photograph: Ian Langsdon/EPA

Signatories to the statement include Article 19, the International Press Institute and the PEN American Center, which faced upheaval last year over its decision to honour Charlie Hebdo as winner of its “freedom of expression courage award”. More than 240 writers put their names to a letter last year claiming the choice was “not simply conveying support for freedom of expression, but also valorising … material that intensifies the anti-Islamic, anti-Maghreb, anti-Arab sentiments already prevalent in the western world”.

“It was important for us to put clearly what is the position of PEN – which is freedom of speech over all,” said Emmanuel Pierrat, the French author and freedom of expression lawyer who has acted for Charlie Hebdo. “[The decision to give the prize to Charlie Hebdo] was contested, but is not contested any more.”

Pierrat added that he liked the anniversary edition cover of the magazine, which represents God as a terrorist bearing a gun, and which has been criticised by the Vatican. “Charlie Hebdo is on the same lines as ever – a line against dictatorship of religion and of ideology,” said Pierrat.

“A year ago today, the Charlie Hebdo staff chose courage and freedom over self-censorship and fear,” said the Mexican-American writer Jennifer Clement, president of PEN International. “All over the world we are experiencing the cruelty of zealots who now have access to military weapons as well as violent repression from state and non-state actors. Because of this, self-censorship is also increasing due to fear.”

“Truth cannot be known and examined without freedom of expression and so freedom of expression is also knowledge. The Charlie Hebdo staff refused to stop their work and dared, in the face of death, to practise freedom of expression, which includes the freedom to laugh.”

• This article was amended on 7 January 2015. In an earlier version, Reporters Without Borders was erroneously included in a list of the signatories to the statement.