Beatrice Fihn, who heads the Geneva-based International Campaign to Abolish Nuclear Weapons (ICAN), hailed an upcoming summit between the United States and North Korean in what Washington hopes will persuade Pyongyang to abandon its nuclear ambitions.
But she said there needed to be more focus on the dangers posed by the United States and other traditional nuclear-armed states, which have recently engaged in "dangerous escalatory activities."
"The new nuclear policies from the United States and Russia that increase the arsenals and create new types of more usable nuclear weapons, these are very dangerous changes," she told journalists in Geneva.
"I think they are equally dangerous as North Korea's nuclear threats," she said.
Five of the world's nine nuclear-armed states -- Britain, China, France, Russia, and the United States -- are parties to the Nuclear Non-Proliferation Treaty (NPT), which will be the subject of a preliminary review in Geneva next week.
But Fihn said they were clearly not respecting their commitments under the treaty, and were all engaged in modernising their arsenals and making nuclear weapons a more central part of their defence strategies.
'Weapons of mass-destruction'
Washington for instance recently decided to upgrade its nuclear weapons arsenal and to complement massive "strategic" bombs with smaller "tactical" weapons, in a move Fihn said would make them easier to use.
She also decried the threatening rhetoric from US President Donald Trump and other leaders of nuclear-armed states.
"We are now seeing some of these states making explicit threats to use weapons of mass-destruction to indiscriminately kill innocent civilians."
Fihn said she welcomed the announcement that Trump would meet with North Korean leader Kim Jong-un within the next two months.
"I think that it is encouraging to see diplomacy rather than threats," she
But she cautioned that it was unclear what kind of concessions North Korea would be willing to make.
"I am wondering what the United States will bring to the table in this sort of negotiation," she said, warning it would be "very hard" to convince Pyongyang to abandon its nuclear weapons programme as Washington and others continue to ramp up their arsenals.
She also suggested that Trump's threats to pull out of the Iran nuclear deal could "send a very worrying message to a country like North Korea."
"Why would you make a deal with a country like the United States who doesn't seem to be interested in finding solutions that work for two parties?" she asked.
ICAN won the 2017 Nobel Peace Prize for its efforts to negotiate a treaty prohibiting nuclear weapons.
On Thursday, Fihn accused the nuclear weapons states of using "very serious threats" to pressure countries not to ratify the treaty, including threatening to cancel aid.
The treaty, which since it was voted through last July has been signed by 58 countries and ratified by seven, needs 50 ratifications before it can enter into force.