United States House of Representatives Speaker Nancy Pelosi reaffirmed in Seoul on Thursday her country's commitment to the denuclearization of North Korea and expressed concern about its weapons activity.

Pelosi met Thursday morning with her South Korean counterpart, Kim Jin-pyo, to discuss regional security and the economic outlook, among other things.

"The two sides expressed concern over the grave situation in which North Korea's level of threat is heightening," Kim said afterwards, reading a joint statement, according to Yonhap news agency.

They were referring to the record number of missile tests carried out this year by Pyongyang and the persistent rumors of an upcoming nuclear test.