A Japanese daily says U.S. intelligence has confirmed North Korea's restart of its experimental nuclear reactor in Yongbyon that it shut down earlier this year to remove spent fuel rods.

The Asahi Shimbun on Tuesday said the North resumed in May the construction of a 50-megawatt reactor in Yongbyon and 200-megawatt reactor in Taechon.

The report said Washington has since enhanced its surveillance on the North via spy satellites on the two locations and confirmed a crane entering the Yongbyon site early this month.

The daily said the U.S. government believes the North's move is apparently intended to strengthen its bargaining power and win more concessions in the upcoming six-way talks in Beijing.