"We are disappointed that the ambassadors from the United Kingdom, the United States and France won't be there," the head of the International Campaign to Abolish Nuclear Weapons (ICAN) Beatrice Fihn told AFP.
"They claim to be committed to a world without nuclear weapons, and they should be celebrating civil society's work on the issue," she said, regretting their "defensive" position, yet noting that it "shows that this treaty and the campaign is already having an impact on them".
The Peace Prize was awarded on October 6th to ICAN, a coalition of non-governmental organisations lobbying for a historic treaty banning atomic weapons, which was signed in July by 122 countries though none of the nuclear powers.
ICAN will formally receive its prize at a lavish ceremony in Oslo on December 10th.
During a meeting in the Norwegian capital last week, the United States, France and Britain all informed the Nobel Institute of their joint decision to be represented by their embassy's second-in-charge.
"They clearly received instructions to express their reservations towards ICAN and the global treaty" to ban weapons of mass destruction, the head of the Nobel Institute, Olav Njølstad, told AFP.
Of the nine countries with nuclear weapons capabilities, Russia and Israel, an unofficial nuclear nation, will be the only ones sending their ambassadors to the ceremony.
"In principle, we like all embassies in Oslo to send their highest representative but we have to accept that, sometimes, for political reasons, various countries abstain from participating or choose to do so at a lower level," Njølstad said.
The United States, France and Britain all confirmed their lower level of participation to AFP.
The US embassy noted the treaty comes "at a time of increased danger of nuclear proliferation".
"This treaty will not make the world more peaceful, will not result in the elimination of a single nuclear weapon, and will not enhance any state's security," it said in a statement to AFP.
Without mentioning North Korea by name, it stressed that "this treaty ignores the current security challenges that make nuclear deterrence necessary", and reiterated Washington's support of the 1968 global non-proliferation treaty.
Britain said meanwhile in a statement to AFP that it "is committed to the long term goal of a world without nuclear weapons".
"We share this goal with our partners across the international community including US and France."
The Nobel Institute said the ambassadors of India and Pakistan will be travelling at the time of the ceremony, while China has not attended the prize-giving since 2010, when a Chinese dissident was awarded the honour.
North Korea does not have an embassy in Oslo.