UPDATE 2-Trump-Kim talks "some weeks" away - Tillerson

(Changes slug, adds background and Russian foreign minister comments)

DJIBOUTI, March 9 (Reuters) - Talks between U.S. President Donald Trump and North Korean leader Kim Jong Un will take some weeks to arrange, U.S. Secretary of State Rex Tillerson said on Friday.

Trump said on Thursday he was prepared to meet Kim in what would be the first face-to-face encounter between any leaders of the two countries. It potentially marks a major breakthrough in easing tensions over Pyongyang's nuclear weapons program.

"President Trump has said for some time that he was open to talks and he would willingly meet with Kim when conditions were right," Tillerson said. "And I think in the president's judgment that time has arrived now."

The decision was made by the president himself, Tillerson said during a visit to Djibouti.

"Now it's a question of agreeing on the timing of the first meeting between the two of them, and that will take some weeks before we get all that worked out."

Trump has derided Kim as a "maniac," referred to him as "little rocket man," and threatened in a speech to the United Nations last year to "totally destroy" North Korea if it attacked the United States or one of its allies.

Kim responded by calling the U.S. president a "mentally deranged U.S. dotard."

Trump's aides have been wary of North Korea's diplomatic overtures because of its history of reneging on international commitments and the failure of efforts on disarmament by previous U.S. administrations.

Some U.S. officials and experts worry North Korea could buy time to build up and refine its nuclear arsenal if it drags out talks with Washington.

Tillerson said the United States was surprised at how "forward-leaning" Kim was in his conversations with a visiting South Korean delegation. He said it was the strongest indication to date of Kim's "not just willingness but really his desire for talks."

Kim has committed to denuclearisation and to suspending nuclear and missile tests, South Korea's National Security Office head Chung Eui-yong said on Thursday after briefing Trump on a meeting South Korean officials held with Kim earlier this week.

China's foreign minister, Wang Yi, called on the United States and North Korea to hold talks as soon as possible, saying that at a news briefing in Beijing on Thursday that things "will not be smooth sailing."

Russia believes that a possible meeting between Trump and Kim "is a step in the right direction," Foreign Minister Sergei Lavrov told reporters while on a visit to Ethiopia. (Reporting by pool reporters, additional reporting by Aaron Maasho in Addis Ababa, writing by Maggie Fick and Katharine Houreld, Editing by Angus MacSwan)