The United States and China are working together for a nuclear-free Korean Peninsula and won't accept North Korea as a nuclear weapons country, U.S. National Security Advisor Susan Rice said Monday.
  

Rice made the remark during a speech previewing a summit between President Barack Obama and Chinese President Xi Jinping, saying the two countries are "united in demanding the complete and verifiable denuclearization of the Korean Peninsula."
  

"We firmly oppose North Korea's efforts to develop nuclear weapons and ballistic missiles that threaten regional stability and our respective national security interests," she said during an address at George Washington University.
  

Rice said China is "a fulcrum of influence" for the North, referring to Beijing's status as the main provider of economic assistance and diplomatic support for Pyongyang.
  

This week's summit between Obama and Xi, set for Friday, will be another opportunity to discuss how we can sharpen Pyongyang's choices between having nuclear weapons and developing economically, Rice said.
  

"Neither the United States nor China will accept North Korea as a nuclear weapons state," she said.
  

The summit comes as tensions on the Korean Peninsula flare anew after the North strongly hinted it would conduct a banned long-range rocket launch, possibly around next month's ruling party anniversary. Pyongyang also said its bomb-making nuclear facilities have returned to normal operation and could conduct a nuclear test if necessary.
  

North Korea has conducted three underground nuclear tests so far, in 2006, 2009 and 2013. The country has also conducted a series of long-range missile or rocket launches since 1998. In its most recent launch in late 2012, the North succeeded in putting a satellite into orbit.
  

Analysts have warned that it is only a matter of time until the North develops nuclear-tipped missiles. Some experts have recently warned that the communist nation's nuclear arsenal could expand to as many as 100 bombs by 2020.
  

Other agenda items for this week's summit are expected to include thorny issues, such as territorial disputes over the South China Sea, cyber-hacking, China's foreign exchange policy, climate change and human rights.
  

"We are steadily and methodically expanding the breadth and depth of our cooperation with China. Our story is, overwhelmingly, one of progress. Still, the reality is we face difficult challenges. And, we never shy away from pressing our concerns,"Rice said.
  

She said the U.S. has urged China to carry out market reforms that level the playing field for foreign firms and refrain from competitive currency devaluation. She also noted that Obama has made clear to Xi that "state-sponsored, cyber-enabled economic espionage must stop."
  

"This isn't a mild irritation. It is an economic and national security concern to the United States," she said of cyber-hacking.

"It puts enormous strain on our bilateral relationship, and it is a critical factor in determining the future trajectory of U.S.-China ties."
  

Speaking of martime territorial disputes, Rice also said that the U.S. takes no position on competing territorial claims, but will continue to stress the importance of preserving "freedom of navigation and commerce through some of the world's busiest sea lanes."
  

"The United States of America will sail, fly and operate anywhere that international law permits," she said. (Yonhap)