WASHINGTON, Nov 1 (Reuters) - North Korea on Tuesday again demanded that the United States and South Korea halt joint military exercises, saying such "rashness and provocation can be no longer tolerated," while the White House said concern remains high about the potential for a North Korean nuclear test.The United States and South Korea began one of their largest combined military air drills on Monday, which will involve hundreds of warplanes from both sides staging mock attacks 24 hours a day for the better part of a week.In denouncing the drills in a statement carried by North Korea's official news agency, Pak Jong Chon, secretary of the Central Committee of North Korea's ruling Workers' Party, warned the United States and South Korea against any attempt to attack."If the U.S. and South Korea attempt to use armed forces against the DPRK without any fear, the special means of the DPRK's armed forces will carry out their strategic mission without delay and the U.S. and South Korea will have to face a terrible case and pay the most horrible price in history," the statement said, using the initials of North Korea's official name.Washington and Seoul believe North Korea may be about to resume testing of nuclear bombs for the first time since 2017 and have embraced a strategy of "deterring" Pyongyang through major military drills that some current and former officials say may worsen tensions."