North Korea's (search) premier, on a tour of sites highlighting China's (search) economic reforms, did not respond Friday to appeals from its closest ally for the North to return to nuclear disarmament talks.

Premier Pak Pong Ju (search) did not speak to reporters after his ride on a magnetic levitation train to Shanghai's international airport and back to its financial district. Before departing the city, Pak pledged to enhance North Korea's economic and trade ties with the city, the official Xinhua News Agency reporte on Washington's demand that Pyongyang renounce nuclear ambitions. The six-nation talks organized by Beijing also include Japan, Russia and South Korea.

A Foreign Ministry spokesman said Thursday that meetings with Pak produced no breakthrough. The spokesman, Liu Jianchao, urged the United States and North Korea to take steps to rebuild trust.

Pak's only reported comment on the appeals came Tuesday when he said that Pyongyang might be willing to return to talks "if the conditions are right," according to China's Foreign Ministry.

Washington has been urging Beijing to use its status as the North's main ally and aid donor as leverage to prod Pyongyang back to talks. Secretary of State Condoleezza Rice recently suggested that Pyongyang might face sanctions if it does not cooperate.

The nuclear dispute flared in late 2002 when Washington said Pyongyang admitted operating a secret nuclear program in violation of a 1994 agreement that gave it oil and other aid in exchange for abandoning nuclear development.

Also on Friday, North Korea's ambassador to Thailand was quoted by a Thai newspaper as saying that Pyongyang was prepared for further talks with the United States but had also made preparations for war. His comments came after North Korea claimed earlier in the week to have expanded its nuclear arsenal to guard against a possible U.S. attack.

"We are ready to talk peace and we are ready for war with the Americans," The Nation quoted O Song Chol as saying in an interview.

Chol said talks could only resume if the United States apologized for labeling his country an "outpost of tyranny" and ended its hostile policy toward North Korea — North Korea's standard demands.