Scotland's biggest book festival has written an expansive new chapter for 2017, with the Edinburgh International Book Festival extending further into the capital's New Town.

In a "response to the 70th anniversary of the festival city" the festival is to have two new venues in George Street - the Bosco Theatre, which will also be used by a promoter in the Fringe, and The Greenhouse - as well as holding events at the King's Theatre and St Mary's Cathedral.

The two new venues on George Street will include writing workshops, live writing, and drop-in activities, as well as its own box office, book shop and seating area, and will "open up the festival to new audiences."

Nick Barley, the director of the festival, unveiling the 2017 programme, said that the festival's expansion in 2017 was an "experiment" but part of an effort to broaden the festival's venues beyond its home of 34 years, Charlotte Square Gardens.

This year's festival is the largest yet in scale, with 1000 authors and more than 800 events, he said, and the two new theatres will be additional to the eight theatres in the square.

"The festival in Charlotte Square remains as before, but we are adding the new venues as an explicit way of reaching out to the city in this anniversary year, to attract new audiences who may not yet have come into Charlotte Square Gardens," he said.

"We will see how things work in 2017, but certainly we can regard this as an important experiment about how the festival can cope with increasing demand, that we are experiencing and have been for a number of years now, and we hope it will lead to new things."

Mr Barley said in future other venues may be beyond the west end of the city but the gardens remains its 'home and its hub'.

He added: "We have not intention of leaving that. But the audience demographic is getting young and broader and we need to accommodate that demand, and we need to look at added venues."

The programme for 2017 features tow of America's leading writers, Paul Auster and Richard Ford as well as the First Minister Nicola Sturgeon in conversation, Limmy, Zadie Smith, David Mitchell as a guest curator, Charlotte Rampling, Val McDermid, Simon Callow, Ian Rankin, Karl Ove Knausgaard, the Nigerian writer Chimamanda Ngozi Adichie, and many others.

Auster is celebrating his own 70th birthday this year, and he is one of nearly 60 US writers, the highest total in its history.

There will also be drama at the festival: in a new partnership with the Royal Lyceum Theatre, the book festival is to make three 45 minutes dramas on a stage in Charlotte Square Gardens, inspired by three books, Amy Liptrot's The Outrun, Graeme Macrae Burnet's His Bloody Project and James Kelman's Dirt Road.

In an event called 'Paul Auster at 70', the author of the New York Trilogy, among many other books, will discuss his life and work at the King's Theatre, while in the cathedral, David Mitchell will be joined by the conductor and pianist David Greilsammer to prevent a new collaboration.

The essayist, novelist and journalist Andrew O'Hagan is to deliver a keynote speech on the future of Scotland, while there will also be an appearance by the Danish author of the bestselling Little Book of Hygge, Meik Wiking.

One of the UK's most successful writers for children, Cressida Cowell, will unveil her new series, The Wizards of Once.

The theme of the 2017 programme for the festival, which runs from August 12-28, is Brave New Words.

Mr Barley added: "Seventy years on from the first Edinburgh Festival, the need for artists and performers to come together in celebration of free speech and the power of creativity is as great as it has ever been.

"Against a backdrop of political earthquakes, this year's Book Festival proudly presents an awe-inspiring international array of writers who are closely observing the changing world and - to paraphrase the poet Emily Dickinson - telling it slant."

A series of events are to be presented under the title This Woman Can, and will feature Yazidi teenager Farida Khalaf who will tell her story of being kidnapped and sold into slavery by Isis, the politicians Harriet Harman, Jess Phillips and Catherine Mayer as well as Juliana Buhring, Dervla Murphy and Jennifer Tough, who all embarked upon long distance cycle rides.

Val McDermid will launch her latest novel, Ali Smith will return with her second book in her seasonal series, and the novelist and poet John Burnside will introduce two new works, while James Robertson will appear with Aidan O'Rourke to share songs and stories.

The festival will also see the return of five writers who the Festival paid to embark on journeys across the Americas.

Each of the writers - Harry Giles, Malachy Tallack, Stef Smith, Kevin MacNeil and Jenni Fagan, will discuss their adventures and works in progress.