U.S. Secretary of State Condoleezza Rice used firm language Saturday to reiterate Washington's demand that North Korea immediately resume six-nation talks to resolve the international standoff over its nuclear weapons programs. But she also expressed skepticism that Pyongyang was prepared to give up its nuclear ambitions. "Let me put it plainly. North Korea should return to the six-party talks immediately if it is serious about exploring the path forward that we and other parties have proposed," Rice said during a two-day visit to Japan. "Our security is jeopardized ... by North Korea's nuclear weapons ambitions," Rice said in a policy speech at Tokyo's Sophia University. "The six-party talks offer the best framework for dealing with this problem." "This is where the North Korean government can find the respect it desires and acquire the assistance it needs if it is willing to make a strategic choice," Rice said. Rice, who left for Seoul later Saturday, also pressed Japan to end a costly boycott on U.S. beef and offered support for Japan's membership in the U.N. Security Council.