Former U.S. President Barack Obama, in a memoir released Tuesday, recalled his frustration with Japan's era of "revolving-door" prime ministers that coincided with his presidency and described one of his former counterparts, Yukio Hatoyama, as "awkward."

"A pleasant if awkward fellow, Hatoyama was Japan's fourth prime minister in less than three years and the second since I'd taken office — a symptom of the sclerotic, aimless politics that had plagued Japan for much of the decade," Obama, who was president for eight years from 2009, said in the book, titled "A Promised Land."

The book is the first of two planned volumes of Obama's presidential memoirs. It was released two weeks after the presidential election in which Republican President Donald Trump was defeated by Democrat Joe Biden, who had been Obama's vice president.