Pyongyang has criticised US-led plans to mark the 50th anniversary of the armistice which ended the Korean War.
Sunday's ceremony is due to be held in the truce village of Panmunjom
North Korea described a ceremony to be held on 27 July in the demilitarized zone which separates North and South Korea as "a very dangerous act".
But the UN Command in South Korea said it was confident that the event, due to be attended by about 200 foreign dignitaries as well as veterans, would go ahead safely.
The deputy chief of staff of the UN Command, Thomas Kane, said that North Korea had not been invited to the ceremony. He said the North planned to hold its own commemoration in Pyongyang on Sunday.
A statement by North Korea on Tuesday took issue with the role of the UN in the allies' ceremony.
"The US should stop its unseemly farce of holding the
commemorative event in the name of the UN Command with no legal justification," the statement said, carried by North Korean news agency KCNA.
Pyongyang argues that the UN mandate for the US' involvement in the Korean War was not legal.
North Korea said Washington was using the UN label to "to
cover up the crimes it has committed in Korea for over half
a century and deceive the international community".
Brigadier General Kane said he did not expect the North's wrath to disrupt Sunday's ceremony.
He said the event in a tent in the truce village of Panmunjom would take place in a "safe and secure environment" that will be "respected by all parties concerned".
Former US Secretary of State Henry Kissinger, New Zealand Prime Minister Helen Clark and US Ambassador Thomas Hubbard are among those expected to attend.
Tensions between Pyongyang and Washington have been especially high since last October when US officials said North Korea had admitted to having a secret nuclear programme, in violation of a 1994 agreement.
In recent weeks, there has been a renewed diplomatic push for multilateral talks to solve the crisis, amid reports that North Korea's nuclear programme may be more advanced than first thought.