SEOUL, South Korea — U.S. Secretary of State John Kerry delivered a stark warning to North Korea today not to test-fire a mid-range missile, while rejecting a new U.S. intelligence report suggesting significant progress in the communist regime’s nuclear weapons program.

Kicking off four days of talks in an East Asia beset by increasing North Korean threats, Kerry told reporters in Seoul that Pyongyang and its enigmatic young leader would only increase their isolation if they launched the missile that American officials believe has a range of some 2,500 miles, enough to reach the U.S. territory of Guam.

“If Kim Jong Un decides to launch a missile, whether it’s across the Sea of Japan or some other direction, he will be choosing willfully to ignore the entire international community,” Kerry sai. “And it will be a provocation and unwanted act that will raise people’s temperatures.”

Kerry said the test would be a “huge mistake” for Kim.

“It will further isolate his country and further isolate his people who are desperate for food and not missile launches,” he warned. “They are desperate for opportunity and not for a leader to flex his muscles.”