Donald Trump’s decision to withdraw the US from the Paris agreement has created serious problems for global efforts to tackle climate change, Ban Ki-moon has said.

The former UN secretary general said Trump’s move was politically damaging to international action to limit carbon emissions and had created difficulties in delivering financial aid from richer to poorer countries to help the latter cope with a warming world.

“United States is a big problem now. I think the United States’ decision to withdraw from this Paris agreement really creates a serious problem,” Ban said in an interview with the Guardian.

“They [the Trump administration] have given serious damage to the political side. All the countries are very serious and concerned about this [the US declaring its withdrawal from the climate deal].”

Although Trump indicated in a recent interview that the US may not leave the global accord, Ban said the remarks were not clear. He said the apparent shift in position may have been the result of lobbying from European leaders such as the French president, Emmanuel Macron.

Ban said he hoped Trump would take better advice. “What President Trump has been saying is politically shortsighted and scientifically based on wrong advice; I don’t know who advised him,” he said.

While Europe has been seen as a champion of global climate talks and international efforts to rein in temperature rises, Ban said he was worried this role could be put at risk by political strife.

“I am concerned because of the divisions that are now happening within the EU, not to mention this Brexit, and political difficulties and issues such as refugees,” he said.

He said he hoped Macron and Angela Merkel would take on a leadership role and he had pressed the French president on the issue during an hour-long meeting in December.

Ban said Britain had a duty to keep up action on climate change despite Brexit. “They [the UK government] still have a political and moral responsibility on this issue,” he said.

The US saying it would withdraw from the Paris agreement had imperilled the $100bn-a-year of climate aid the world’s richest countries have pledged to the poorest by 2020, Ban said.

“Without the US, we have a lot of difficulties, particularly mobilising financing,” he said, adding that he was particularly concerned about the one-third of funding the US would normally provide to committees administering billions of dollars in climate money.

“Who will make up all this losses which will not be paid by the US? That’s a serious problem now,” he said.

He said the private sector may have to play a greater role than previously envisaged, and he was working with the World Bank president, Jim Yong Kim, the former UN secretary general Kofi Annan and the former UN climate chief Christiana Figueres to address the challenge.

Despite these setbacks to climate action, Ban said he was encouraged that China was still fully committed to reducing emissions. “President Xi Jinping clearly mentioned that China is fully onboard, understanding that the climate is changing,” Ban said of a meeting with the Chinese leader in November.

Another promising sign was the We Are Still In campaign, a group of US cities, states and businesses that have pledged to stick to the Paris targets regardless of Trump. “This is a groundswell of people,” Ban said.

He said he would dedicate his life beyond the UN to continuing climate change advocacy.

Despite the US’s backtracking, Ban said he remained confident the world could meet the target of limiting temperature increases to less than 2C above pre-industrial levels, and the aspiration to keep them under 1.5C. “I am quite optimistic we will make it happen,” he said.

Ban was recently appointed president of the Seoul-based Global Green Growth Institute, which he hopes to expand beyond its 28 member countries.