By BURT HERMAN – 51 minutes ago SEOUL, South Korea (AP) ― Less than a week after a soaring symphony raised hopes of detente on the Korean peninsula, North Korea leveled its latest tirade Monday against the U.S. military presence in South Korea to dash expectations of quick progress in its nuclear standoff. In a further setback, the main U.S. negotiator to the long-running arms talks with the North headed home Monday after lingering in the region for days following the New York Philharmonic's historic performance in Pyongyang last week ― and failing to win a meeting with his North Korean counterpart. U.S. officials had warned the goodwill generated by the emotional concert would be meaningless without the North fulfilling its requirements under an international accord reached last year. In exchange, the North is to receive aid and political concessions, including removal from U.S. terrorism and sanctions blacklists. The reclusive regime promised in October to lay out its long history of nuclear weapons development in a formal declaration by the end of 2007, a step toward eventually giving up its atomic bombs and the means to make them. Washington says the North has not yet handed over its nuclear list, and U.S. Assistant Secretary of State Christopher Hill pressed Pyongyang Monday to move quickly on the declaration. "Time is short, and I would hope we could get on with that this month," Hill told reporters during a visit to Vietnam before he was to depart for Washington later Monday. One sign of possible progress came over the weekend with news that North Korean leader Kim Jong Il visited the Chinese Embassy in Pyongyang at the request of Ambassador Liu Xiaoming who "conveyed the regards" of Chinese President Hu Jintao, according to the North's official Korean Central News Agency. China is the host of the six-nation talks on the North's nuclear programs, and Washington has often turned to Beijing to help persuade its communist ally to disarm. After the Philharmonic's concert, the North's state media ran brief reports last week that focused on the performance, but the communist government has made no comment on what impact the event might have on the country's strained relations with the outside world. In the North's first official comment since the Philharmonic concert, the government heaped criticism on ongoing U.S.-South Korean military exercises. The war games, which began Sunday, have already been targeted with a verbal barrage from North Korea's million-strong military, but the comment Monday from the country's Foreign Ministry represents the highest form of communication from the regime. The North regularly condemns such exercises as a rehearsal for invasion. The United States ― which deploys about 28,500 troops in the South, a legacy of the 1950-53 Korean War that ended in a cease-fire that lingers unresolved to this day ― denies it has any plans to attack. The North's Foreign Ministry said the military maneuvers demonstrate Washington "is invariably sticking to its hostile policy to stifle the (North) by force." The presence of a nuclear-powered aircraft carrier and submarine in the exercises amounts to a "nuclear threat and blackmail" that "will only put a brake on the process of the denuclearization of the peninsula," the ministry said in the statement carried by KCNA. In response, the country warned it would "take necessary countermeasures including those to further bolster up all its deterrent forces" ― a reference to its own nuclear arsenal. Andrei Lankov, an expert on the North who studied there and is a professor at Seoul's Kookmin University, said the absence of such inflammatory statements from the Pyongyang regime would be a sign that a "revolution has begun in North Korea" and a "dramatic break with the past, which is very unlikely to happen anytime soon." It would be unreasonable to expect any such change before a decade, he said, following a long series of exchanges like the Philharmonic's concert in the North. "Just one concert will do more or less nothing. It's good, but it's just a small drop; there should be many such drops," Lankov said.