OTTAWA -- The unfolding North Korean nuclear crisis is exposing Justin Trudeau's Liberal government to international criticism that it is too soft on nuclear disarmament -- and too close to the sabre-rattling Trump administration.

International anti-nuclear activists call it a development that could have ominous implications for the government's bid to win a temporary seat on the United Nations Security Council in 2019.

Trudeau called on the Security Council to take "decisive action" against North Korea following Sunday's report of a nuclear detonation by Pyongyang -- the latest in a summer of provocations on the Korean Peninsula.

However, Canada has not supported a broader effort by the full UN General Assembly to create a treaty that would outlaw nuclear weapons, a document that opens for signing when world leaders meet in New York later this month.

More than 120 countries support the treaty, and with Canada seeking a temporary seat on the UN Security Council in 2019, two international anti-nuclear groups say Canada's stance could hurt its ability to win a seat.

Countries vying for a seat on the UN's most powerful body need the support of at least 128 countries in the General Assembly.

The treaty has no support among the countries that actually have nuclear weapons, including the United States, and their military allies, including NATO and Canada.

"While we've seen a lot of nice words come out of the Trudeau government, policies haven't really followed -- not on nuclear weapons, and not on other weapons issues that Canada has traditionally led on," Beatrice Fihn, the head of the International Campaign to Abolish Nuclear Weapons, said Tuesday from Geneva.

"Even if you're in a military alliance, your military alliance can't be based on having to support Donald Trump's threats to use weapons of mass destruction."

Having a strong position on disarmament that is distinct from the five permanent members of the Security Council -- all of which have nuclear weapons -- can play an important role in campaigning for a temporary two-year seat on the body, she said.

"Having a solid reputation as a not-a-puppet-of-the-U.S. is obviously going to be something to your advantage in a Security Council campaign."

The Trudeau government is in the same tight spot as all of its fellow non-nuclear NATO countries: nuclear weapons are at the core of the alliance's defence policy, said Alyn Ware, the founder of Parliamentarians for Nuclear Non-Proliferation and Disarmament.

If Canada supported the Treaty on the Prohibition of Nuclear Weapons, it would undermine NATO's strategic doctrine and place Canada at odds with the alliance, said Ware, whose group is based in Hamburg, Germany.

NATO solidarity could have consequences in a future Security Council vote, Ware said in an interview Tuesday.

"When it comes to the Security Council, you need the vote in the General Assembly, and in the General Assembly, the majority of countries are anti-nuclear."

Adam Austen, a spokesman for Foreign Affairs Minister Chrystia Freeland, said Canada supports "concrete" and "meaningful" steps towards disarmament. He cited Canada's push to revive the Fissile Material Cut-off Treaty, which would be designed to rid the world of the key bomb-making ingredients.

The government also supports an initiative by Norway to "create a group of governmental experts on nuclear disarmament verification, one of the most challenging obstacles to nuclear disarmament," he said in an email.

Fihn, Ware and others say Canada needs to do more, including working within the NATO alliance to soften its nuclear policy.

"I don't think Canada belongs on the Security Council unless it wants to do the right thing by signing the treaty," said Metta Spencer, a Canadian disarmament advocate and editor of the quarterly Peace magazine.

"Canada could sign the treaty, but with a statement that we're staying inside NATO and we're working to get NATO to change its policy."

Douglas Roche, a former Canadian senator and disarmament ambassador, said Canada's highest foreign policy goal should be to sign the treaty and push for NATO to rid itself of nuclear weapons.

"A moment in history has arrived in which Canada will have to decide if it supports nuclear deterrence or nuclear abolition."