New U.S. Defense Secretary James Mattis will not ask Japan and South Korea to pay a bigger share of the expenses associated with hosting U.S. forces when he visits the two key Asian allies this week, according to Japanese and U.S. government sources.

Pentagon spokesman Jeff Davis meanwhile said the purpose of Mattis' visit to South Korea on Thursday and Japan on Friday and Saturday is "not to roll out any big changes in U.S. policy."

"It will mostly be a chance for him to listen, meet the parties involved there ... and make sure we're positioned, going forward, to be able to continue the strong alliances we have," Davis told reporters Monday, referring to Mattis, a retired Marine Corps general.