A senior South Korean official says the stalled six-party nuclear talks are likely to resume at the end of May.

The official, who is visiting the United States to discuss the North Korean nuclear issue, also said Wednesday the U.S. is cautiously optimistic that the talks will yield progress.

He said Washington has begun to look at the North in a positive way after assessing that it has become more sincere. The official said the assessment was based on recent developments, including a visit to Pyongyang by State Department official Sung Kim.

The official was quick to add, however, that Pyongyang and Washington must settle several working-level problems before the North makes its nuclear declaration.