A coalition of European Greens have urged the US Green party’s nominee, Jill Stein, to pull out of next week’s election and endorse Kamala Harris to stop Donald Trump from becoming president.

Green parties in 16 European countries from Portugal to Ukraine distanced themselves from their US counterparts in a statement on Friday, and called for Stein to withdraw from the race.

“We are clear that Kamala Harris is the only candidate who can block Donald Trump and his anti-democratic, authoritarian policies from the White House,” they wrote.

The signatories include Green parties from several countries in which they govern as part of coalitions, such as Germany, Ireland, Belgium and Spain. The parties said there was “no link” between the Greens in Europe and the US.

“The US Greens are no longer a member of the global organisation of Green parties,” they wrote. “In part, this fissure resulted from their relationship with parties with authoritarian leaders, and serious policy differences on key issues including Russia’s full scale assault on Ukraine.”

The US electoral college system disadvantages small parties such as the Greens, which attract 1-2% of support in opinion polls. But their influence could still sway the overall outcome by drawing away support for the two main parties in key battleground states.

As of 30 October, polls put Harris at 47% and Trump at 46% – but analysis shows even minute shifts in voter behaviour can decide who ends up in the White House.

In the US, the Green party has been called “not serious” by Alexandria Ocasio-Cortez, the progressive Democratic congresswoman from New York. “All you do is show up once every four years to speak to people who are justifiably pissed off, but you’re just showing up once every four years to do that, you’re not serious,” Ocasio-Cortez posted on Instagram last month. “To me, it does not read as authentic. It reads as predatory.”

The US Greens said the European Greens were reiterating “intense partisan invective, smears, misinformation, and Democratic Party talking points.” They criticised the Democrats for increasing oil and gas production and providing military aid to Israel.

They also suggested the US Greens were drawing support from people who had no desire to vote for either of the two main candidates.

“European Greens can endorse whomever they please in a US election but we invite them to communicate directly with us to understand our positions and participation in elections, and to support our demand for a national popular vote by ranked-choice voting (RCV) for president, which would eliminate the alleged spoiler factor.”

“The Democratic Party has ignored and rejected this demand, which leads us to suspect that Democrats would rather lose to Republicans like Trump than tolerate the presence of more than two parties in US elections.”

Trump has dismissed the climate crisis as a hoax and promised to scrap spending on clean energy while unleashing a wave of oil and gas expansion.

During Trump’s last term in office, the US became the first country in the world to pull out of the 2015 Paris agreement on climate change. The UN secretary general, António Guterres, in an interview with the Guardian on the sidelines of a biodiversity summit in Colombia this week, , compared the prospect of a second US departure from the treaty to losing a limb but surviving.

“We don’t want a crippled Paris agreement,” he said. “We want a real Paris agreement.”