Rice, on her first tour of Asia since taking office, said North Korea could only realise its wishes for security assurances and aid if it ended its boycott of six-nation talks on its nuclear ambitions.
"North Korea should return to the six-party talks immediately if it is serious about exploring the path forward that we and the other parties have proposed," Rice said in a speech at Sophia University in Tokyo.
"This is where the North Korean government can find the respect it desires and the assistance it needs if it is willing to make a strategic choice," she said.
North Korea last took part in the talks in June 2004 and in February announced a new suspension of dialogue, demanding Rice apologise for calling the communist state an "outpost of tyranny".
Rice in her speech refrained from such denunciations of Pyongyang, but said she sympathised with the plight of the North Korean people and the people kidnapped by North Korean agents.
Japan is embroiled in a separate row with North Korea and has threatened economic sanctions after Pyongyang allegedly sent false evidence to prove a number of Japanese people it had kidnapped to train its spies were dead.
"North Korea should return to the six-party talks immediately if it is serious about exploring the path forward that we and the other parties have proposed"
US secretary of state
The talks on the nuclear programme include the two Koreas, the United States, China, Russia and Japan, but Rice said a special responsibility lay with Beijing, which is Pyongyang's main ally.
"China has a particular opportunity and responsibility here and I will soon be discussing in Beijing how the United States and China can advance our common interests on this and others," Rice said.
Rice, who heads to Beijing on Sunday at the end of her Asian tour, called for China to embrace democracy as its economy surged.
"Time and again we have seen that economic and political openness cannot long be separated. Even China must eventually embrace some form of open genuine representative government if it is to reap the benefits and meet the challenges of a globalising world," Rice said.
"Clearly, America has reason to welcome the rise of a confident, peaceful and prosperous China. We want China as a global partner able and willing to match its growing capability to its international responsibility," she said.
"Even China must eventually embrace some form of open genuine representative government if it is to reap the benefits and meet the challenges of a globalising world"
US secretary of state
But she added: "Of course issues that complicate our cooperation with China, particularly Taiwan."
China on Monday passed a law giving it the legal means to attack Taiwan - where the nationalists fled in 1949 after losing China's civil war to the communists - if the island moves to outright independence.
Rice said the United States stood behind its policy of considering Taiwan part of the mainland.
Japan has seen rising friction with China as both Tokyo and Beijing play greater global roles, with officially pacifist Japan on a historic military mission in Iraq.
"Japanese leadership in advancing freedom is good for the Pacific community and good for the world," Rice said.
She called on the United States and Japan to develop a formal way to coordinate their foreign aid. A US official accompanying Rice said the two countries provided more than 40% of the governmental assistance to developing countries.
But bilateral relations have also seen strain over Japan's ban on US beef imports over fears of mad cow disease.
Japan was the top market for US beef before the suspension in December 2003. US members of Congress have called for sanctions unless the multi-billion-dollar trade resumes quickly, but Japan has insisted its experts will not be rushed in finding a way to test US beef.
Rice(L) met with her Japanese
counterpart Nobutaka Machimura
"The time has come to solve this problem," Rice said.
"There is a global standard on the science involved and we must not let exceptionalism put at risk our ability to invest and trade our way to even greater shared prosperity," she said.