SEOUL (Reuters) - North Korea held mass rallies in Pyongyang where people shouted slogans vowing a "war of revenge" to destroy the United States, as it marked the 73rd anniversary of the outbreak of the Korean War, state media reported on Monday.

About 120,000 working people and students took part in the rallies held across the capital on Sunday, state news agency KCNA reported.

Photos released by state media showed a stadium crowded with people holding placards reading "The whole U.S. mainland is within our shooting range" and "The imperialist U.S. is the destroyer of peace."

Sunday's anniversary came amid concerns Pyongyang could soon conduct another launch of its first military spy satellite to boost monitoring of U.S. military activities after its first attempt ended in failure on May 31.

North Korea now had "the strongest absolute weapon to punish the U.S. imperialists" and the "avengers on this land are burning with the indomitable will to revenge the enemy," KCNA said.

Nuclear-armed North Korea has been testing various weapons including its biggest intercontinental ballistic missile, ramping up tension with the South and the South's main ally, the United States.

In a separate foreign ministry report, North Korea said the U.S. was "making desperate efforts to ignite a nuclear war," accusing Washington of sending strategic assets to the region.

North and South Korea remain technically at war because their 1950-53 conflict ended in a truce, not a treaty.

(Reporting by Soo-hyang Choi; Editing by Stephen Coates)