Salman Rushdie is to take part in this year's Edinburgh International Book Festival after a 20-year absence.

Organisers of the world's largest literary festival said they were overjoyed to welcome Rushdie back to Edinburgh and would take whatever steps necessary to protect the author, who was subjected to death threats over his book the Satanic Verses.

Rushdie will appear alongside other literary heavyweights such as Margaret Atwood, Dario Fo, Doris Lessing, John Irving and Andre Brink. They are among 500 writers who will take part in this year's festival, which runs from August 13 to 29.

The festival director, Catherine Lockerbie, speaking at the launch of the programme yesterday, said the 2005 event would be more political than previous years, exploring issues such as nationhood, freedom of expression and relations between east and west. There will also be a special emphasis on writers from Russia and Canada.

Rushdie will discuss his new work, Shalimar the Clown, due to be published in September. Tickets for his appearance are likely to sell out within hours.

"I am overjoyed to welcome him back after an over long and enforced absence," said Ms Lockerbie. "He has far more freedom of movement these days. He is not in hiding. He is coming to the festival and whatever requires to be done we will do it."

She said Rushdie's presence was proof of the power and importance of the written word.

"We are really asserting the primacy of freedom of expression. I think it's vital because we function as a forum where people can talk about things that matter. I think that's why our audience has grown so fast ... because people are hungry for some substance."

Other participants include Anna Politkovskaya, the Russian journalist who helped mediate in the Moscow theatre siege and was later allegedly poisoned on her way to help negotiate in the Beslan siege.

Zadie Smith will appear in advance of the launch of her novel, On Beauty, and Irving returns with Until I Find You, a novel partly set in Edinburgh which features an organist addicted to tattoos.

Clare Short is one of a handful of British political figures appearing the event, including Tony Benn and Neil Kinnock. Andrew Marr and Rageh Omar will also speak.

Last year, the festival attracted 200,000 people.