Meryl Streep, JK Rowling and Zadie Smith have all added their names to an open letter calling on the United Nations to investigate the death of the journalist Jamal Khashoggi.

More than 100 artists, writers and activists have shown support on the international day to end impunity for crimes against journalists, a month after the Washington Post journalist was killed at the Saudi consulate in Turkey.

“The violent murder of a prominent journalist and commentator on foreign soil is a grave violation of human rights and a disturbing escalation of the crackdown on dissent in Saudi Arabia, whose government in recent years has jailed numerous writers, journalists, human rights advocates and lawyers in a sweeping assault on free expression and association,” the letter reads.

It’s addressed to António Guterres, the UN secretary general, and calls on him to initiate an independent investigation into what really happened to Khashoggi. Since his disappearance, Turkish officials have said they have evidence that he was dismembered and his body was dissolved by a squad of Saudi assassins. Yet Saudi officials still claim it was the result of a fistfight and an interrogation gone wrong.

“The murder of a journalist inside a diplomatic facility would constitute nothing less than an act of state terror intended to intimidate journalists, dissidents and exiled critics the world over,” the letter reads.

Other names in the list of signatories include Patrick Stewart, Ian McEwan, Bob Woodward, Roxane Gay, Margaret Atwood, Alec Baldwin, Molly Ringwald, Colm Tóibín and Jeffrey Eugenides. The group was assembled by Pen America, a not-for-profit organisation aimed at defending freedom of expression.

Before his death, Khashoggi had been critical of the Saudi crown prince, Mohammed bin Salman, who was this week revealed to have called him a “dangerous Islamist” in a phone call with Jared Kushner, the White House adviser and son-in-law to Donald Trump, just before Turkish police said they believed the missing journalist was dead.