WASHINGTON (Reuters) - The author of a deeply critical book about Donald Trump’s first year in office said on Friday he had spoken with the president while working on it, contradicting Trump’s assertion that he had never talked to the writer for the book and had not authorized any access to the White House.

Michael Wolff’s book “Fire and Fury: Inside the Trump White House” was an instant bestseller on Friday, its release pulled forward after published excerpts this week set off a political firestorm, threats by Trump lawyers of legal action and an effort to halt publication.

The book, dismissed by Trump as full of lies, depicts a chaotic White House, a president who was ill-prepared to win the office in 2016, and Trump aides who scorned his abilities. Standing by his reporting, Wolff told NBC on Friday that Trump aides had all told him they viewed him as child-like.

“I absolutely spoke to the president. Whether he realized it was an interview or not, I don’t know, but it was certainly not off the record,” he said on NBC’s “Today” program. Wolff added that he had spoken to people who spoke to Trump on a daily, “sometimes minute by minute” basis.

Asked to clarify what he meant when he wrote that Trump’s entire circle questioned his fitness for office, Wolff said, “100 percent of the people around him ... They all say he is like a child.”

On Thursday evening, Trump tweeted, “I authorized Zero access to White House (actually turned him down many times) for author of phony book! I never spoke to him for book.”

“Full of lies, misrepresentations and sources that don’t exist,” Trump added.

The early excerpts have also caused a public rift between the president and his former chief strategist and top campaign aide, Steve Bannon, over Bannon’s comments in the book about Trump and his family.

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BEST-SELLER ON DAY ONE

Lawyers for Trump had called on the book’s publisher, Henry Holt & Co, to halt the book’s release, originally scheduled for Tuesday. Instead, it began sales early and on Friday, its first day in stores, “Fire and Fury” was the top-selling book on Amazon.com.

In Washington, customers lined up in bitterly cold weather to purchase a copy at KramerBooks, which began selling copies at midnight. Many Washington-area bookstores, including KramerBooks, reported selling out of copies as of Friday morning at 10 a.m. ET (1500 GMT).

Justin Bethel, manager of the Politics and Prose bookstore, said its 30 copies sold out quickly. “It got so we couldn’t answer the phone, it was ringing so much,” he said.

Politics and Prose customer Daniel Zhang, 22, said he and his housemate read a chapter online on Thursday night and he planned to read the book later on Friday. “I’m going to finish work, and then I’m not going out tonight; I’m just going to go back and read this book,” said Zhang.

The reaction was less frenetic in New York, Trump’s old home base. Book Culture, an independent book seller in the Upper West Side neighborhood, said on Friday morning four people had bought the book and it had about 160 copies available, with 150 copies available in its other store.

The White House has said the book is riddled with errors, and campaign and administration officials have disputed events depicted in the book.

Spokeswoman Sarah Sanders, who has called the book trash, said again on Friday that Wolff had talked only briefly to the president and did not have wide access.

“This is a guy who made up a lot of stories to try to sell books,” Sanders said in an interview on Fox News Channel.

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In a tweet on Friday, Trump called the book another attempt to smear him since any collusion between his election campaign and Russia “is proving to be a total hoax.”

Special counsel Robert Mueller is investigating possible collusion as part of a broader probe into alleged Russian meddling in the 2016 election. He has not announced any conclusions.

“The Fake News Media (Mainstream) and this phony new book are hitting out at every new front imaginable,” Trump wrote.

Charles Harder, Trump’s personal lawyer, in a legal notice provided to Reuters, warned on Thursday of possible claims including libel against Wolff and Henry Holt & Co and threatened to try to block publication of the book. Harder also told Reuters that “legal action is imminent” against Bannon.

Bannon’s reaction to the controversy has been muted. In interviews after the news broke with the conservative Breitbart News website, he called Trump a “great man” and pledged continued support for the president’s agenda.