Buying the British and Commonwealth rights to the Sherry Jones novel last week, Mr Rynja described it as a "moving love story".
But the radical cleric Anjem Choudhary said the book was an insult to the Prophet Mohammed's honour, something he said would warrant a "death penalty" under Sharia law.
...the radical cleric Anjem Choudhary, who lives in Ilford, east London, said he was "not surprised at all" by the attack and warned of possible further reprisals over the bookUnbelievable.
"It is clearly stipulated in Muslim law that any kind of attack on his honour carries the death penalty," he said.
"People should be aware of the consequences they might face when producing material like this. They should know the depth of feeling it might provoke."
He denied any involvement in the attack but said he "understood" the feelings of the perpetrators.
"If the publication goes ahead then I think, inevitably, there will be more attacks like this - this is the thin of the wedge," he said.
Speaking from Lebanon, the radical cleric Omar Bakri, added: "If anybody attacks that man I cannot myself condemn it.