PYONGYANG, Oct 10 (Reuters) - Isolated North Korea marked the 70th anniversary of its ruling Workers' Party on Saturday with a massive military parade overseen by leader Kim Jong Un, who said his country was ready to fight any war waged by the United States.
Thousands of troops stood at attention under a blue autumn sky in Pyongyang's main Kim Il Sung Square, named after Kim Jong Un's grandfather and the founder of the nation, as Kim, appearing relaxed and confident, made his speech, leaning heavily on the lectern.
The young leader was accompanied by senior Chinese Communist Party official Liu Yunshan, with whom he was seen speaking throughout the event and occasionally sharing laughs, and flanked by senior North Korean party and military officials.
"The party's revolutionary armament means we are ready to fight any kind of war waged by the U.S. imperialists," Kim said in a speech strikingly more forceful than previous public comments, praising the feats of past leaders and the ruling party.
While the White House declined to comment, the Pentagon on Saturday called on Pyongyang to refrain from provocative behavior and said it was closely monitoring the situation on the Korean Peninsula.
"We are in close contact with our Republic of Korea allies and remain committed to the defense of the ROK," Pentagon spokesman Commander Bill Urban said, using to South Korea's official name. "Recent provocative statements heighten tensions, and we call on Pyongyang to refrain from actions and rhetoric that threaten regional peace and security."
Kim made no direct mention of the country's nuclear program, likely a conciliatory diplomatic gesture toward China, which hosted the now-defunct "six-party talks," also involving the United States, on giving economic incentives to Pyongyang in return for scrapping its atomic ambitions.
On Wednesday, a high-level U.S. military official said Washington believed North Korea had the capability to launch a nuclear weapon against the U.S. mainland and stood ready to defend against any such attacks.
Kim's speech was followed by troops marching in formation, first by a corps of soldiers dressed in the style of the revolutionary force that fought Japan during World War Two, and then a procession of military might rolling past the square.
A battery of the North's intercontinental ballistic missiles was the highlight of the weapons display, although they are not known to have been successfully tested.
Impoverished North Korea and rich, democratic South Korea remain technically at war after their 1950-53 conflict ended in a truce, not a treaty. The North, slapped with U.N. and U.S. sanctions for its nuclear weapons and rocket programs, often threatens to destroy the South, and its major ally, the United States, in a sea of flames.
In a letter delivered by Liu, the most senior Chinese official to visit Pyongyang since leader Kim came to power following his father's death in 2011, Xi said China attached vital importance to its relationship with North Korea, China's official Xinhua news agency said.
China is North Korea's chief ally and its main trading partner, although ties have been strained over the North's nuclear program.
Xi said in the letter that China had "been striving to treat the bilateral relations from a strategic and long-term perspective." Liu reiterated China's position that it wanted an early resumption of the six-party talks.
"The Chinese side is willing to seek closer communication and deepen cooperation, pushing for a long-term, healthy and stable development of the Sino-DPRK ties," Xi said in the letter cited by Xinhua, referring to North Korea by its official name, the Democratic People's Republic of Korea.
Kim, who is in his early thirties, told the visiting Chinese delegation on Friday that North Korea was also keen to bolster ties, the North's official KCNA news agency said on Saturday.
Liu is the fifth-ranked member on China's ruling Communist Party's elite Politburo Standing Committee. (Additional reporting by Phil Stewart in Washington, Jack Kim and Hooyeon Kim in Seoul, Kazunori Takada in Shanghai and Megha Rajagopalan in Beijing; Editing by Tony Munroe and Nick Macfie)