Image copyright AP Image caption Harper Lee, 88, is said to be hard of hearing and almost blind

Author Harper Lee has dismissed concerns that she is being pressured into releasing a "lost" novel.

The new book, entitled Go Set A Watchman, is her first since 1960's To Kill A Mockingbird, which sold more than 40m copies around the world.

But some have suggested the reclusive 88-year-old is being manipulated into releasing the decades-old manuscript.

Lee responded in a statement, saying: "I'm alive and kicking and happy as hell with the reactions to Watchman."

News of the author's second novel was greeted with astonishment on Tuesday.

Written before To Kill A Mockingbird, it features many of the same characters, with an adult Scout Finch returning to her native Alabama from New York to visit her father.

The novel was believed to have been lost until recently, when Lee's lawyer, Tonja Carter, discovered it amongst the author's effects.

Image copyright AP Image caption To Kill A Mockingbird won a Pulitzer Prize and was adapted into an Oscar-winning hit film, starring Gregory Peck

But some were sceptical about the timing of the announcement, which came months after the death of Lee's sister, Alice, a lawyer who had shielded her younger sibling from the outside world.

Alice, who died last November aged 103, wrote in 2011: "Harper can't see and can't hear and will sign anything put before her by anyone in whom she has confidence."

But a spokesman for Penguin Random House said: "Harper Lee still enjoys reading and uses a magnifying machine from the New York Institute for the Blind to read books, newspapers and documents."

Harper, who resides in an assisted living facility in Alabama, also suffered a stroke in 2007.

Actress Mia Farrow was among the first to raise concerns, ‏tweeting: "Is someone taking advantage of our national treasure, 88-year-old Harper Lee?"

Writer Madeleine Davies also questioned whether the book was "willingly given", while novelist Tracy Chevalier told the BBC Radio 4's Today programme she was "just a little concerned that Harper Lee may have been pressured into this".

Lee's international rights agent Andrew Nurnburg issued a statement, acknowledging the "speculation" but reassuring readers that Lee was fully behind the project.

"I met with her last autumn and again over two days in January; she was in great spirits and increasingly excited at the prospect of this novel finally seeing the light of day," he said.