The United States says it cannot take diplomatic strides forward with North Korea until the North improves its ties with South Korea. 

Speaking at a congressional hearing Thursday, U.S. Acting Deputy Assistant Secretary of State for East Asia and Pacific Affairs, James Zumwalt, said "U.S.-North Korea relations cannot fundamentally improve without sustained improvement in inter-Korean relations." 

Zumwalt said that, despite the North's overtures in the region and outreach to counterparts in the six-party process, the U.S. has yet to see concrete steps suggesting North Korea is prepared to negotiate on the key issue of the verifiable denuclearization of the Korean Peninsula.

Zumwalt added Washington remains gravely concerned about the deplorable human rights situation in the North, and is mulling ways to further pressure Pyongyang to improve its human rights record.