The North's official Korean Central News Agency (KCNA) reported that its permanent representative at the UN sent the letter on Friday, the latest protest against the 10-day Ulchi Freedom Guardian exercise set to end Thursday.
"The DPR Korea strongly requests the UNSC to discuss the issue of the joint military exercises as an emergency agenda item," the KCNA reported, using the North's official name, the Democratic People's Republic of Korea, Yonhap news agency reported.
"Should the UNSC ignore the request from the DPR Korea once again, it will become self-evident that the UNSC has ceased to remain as a body that assumes the primary responsibility for the maintenance of international peace and security," it added.
The news agency also said that the military drills are "nothing short of hysteric conduct to add fuel to the raging flames," and accused Washington of pursuing "its evil intention of occupying the North by force."
Pyongyang has long responded furiously to the allies' regular defensive military drills, calling them a "rehearsal for a war of invasion."
The report came a day after the North launched at least three missiles into the East Sea, resuming its provocative acts after a month-long hiatus.