U.S. President Barack Obama says it will take some time to resolve North Korea’s nuclear issue given Pyongyang’s unstable political situation.

In an interview with Reuters on Monday ahead of his trip to Asia, Obama said that neither North Korea nor Iran seem to be stable enough politically to make quick decisions on their nuclear issues.

Obama added, however, that he would strongly argue that more progress has been made on the two nation’s nuclear issues over the last several months than has been seen in the last several years.

He said, in particular, that thanks to unexpected cooperation from China, tougher U.N. sanctions have been placed on the North.