With the United States virtually isolated on the world stage, a string of administration officials went on the offensive Friday to justify the Republican president's decision to abandon the 195-nation Paris deal curbing global emissions.

Trump's top climate advisor Scott Pruitt was indignant: "The world applauded when we joined Paris. And you know why? I think they applauded because they knew it would put this country at a disadvantage."

"The European leaders, why do they want us to stay in? They know it will continue to shackle our economy," said Pruitt, who serves as Trump's Environment Protection Agency administrator.

That combative tone came amid a wave of bitter condemnation from around the world and as Trump and his aides refused to say whether he believes climate change is real, in line with the global scientific consensus.

Trump ignored the question when asked by journalists during an unrelated event with law enforcement officers, although he did joke that Thursday's decision had proven "controversial."

Along with Trump, Pruitt and White House press secretary Sean Spicer were among those who refused to answer repeated questions on the subject.

Instead, Pruitt lashed out, saying "we have nothing to be apologetic about as a country," despite the United States being the world's second-largest emitter of greenhouse gases after China.

"We have taken significant steps to reduce our CO2 footprint," he said.

"Truly, Paris at its core was a bunch of words committed to very, very minimal environmental benefit and costs this country a substantial amount of money."

That message is likely to play well with Trump's Republican base, which reveled in defeating what Pruitt called the "environmental left" and "climate exaggerators."

- Backlash at home -

Expressions of shock and regret poured in from around the world, including from Pacific islands at risk of being swallowed by rising seas, who accused Washington of "abandoning" them.

As well as world outcry, Trump's decision has already prompted a domestic backlash, with state governors, city mayors and powerful companies drawing up plans to meet the Paris pact's greenhouse gas emission targets.

"Here's what is most important for the world to understand: In the US, emission levels are determined far more by cities, states, and businesses than they are by our federal government," said former New York mayor Michael Bloomberg.

German Chancellor Angela Merkel, the EU's most powerful leader, pledged "more decisive action than ever" to protect the climate after Trump's "highly regrettable" decision.

In Brussels, European Council President Donald Tusk said the EU is "stepping up our cooperation on climate change with China" following a summit with Chinese Premier Li Keqiang, although EU officials said the two sides failed to endorse a joint statement due to a separate trade row. 

India's environment minister Harsh Vardhan also said his country is committed to the Paris accord "irrespective" of the position of other nations.

- 'Nothing to renegotiate' -

In a nationalistic "America First" announcement from the White House Rose Garden on Thursday, Trump said he was withdrawing from a UN-backed deal that imposes "draconian financial and economic burdens" on the United States while going too easy on economic rivals China, India and Europe.

"We don't want other leaders and other countries laughing at us anymore. And they won't be."

Trump offered no details about how, or when, a formal withdrawal would happen. At one point he suggested a renegotiation could take place, an idea that was unceremoniously slapped down by partners.

"There is nothing to renegotiate here," EU climate commissioner Miguel Arias Canete told reporters in Brussels.

Nicaragua and war-torn Syria are the only countries not party to the Paris accord, the former seeing it as not ambitious enough.

White House officials acknowledged that under the deal, a formal withdrawal might not take place until after the 2020 election, and leaders will certainly push Trump to reconsider his decision in the meantime.

- Echoes of reality TV -

The 70-year-old Trump gave his decision a reality TV-style tease, refusing to indicate his preference either way until his announcement.

Opponents of the pullout -- said to include Trump's daughter Ivanka -- had warned Washington's global leadership role was at stake, along with the environment.

A dozen large companies including oil major BP, agrochemical giant DuPont and tech heavyweights Google, Intel and Microsoft had urged Trump to stick to the pact.

Following the announcement Tesla boss Elon Musk and Disney chief Robert Iger said they would no longer participate in presidential business councils.

Trump's announcement comes less than 18 months after the climate pact was adopted, the fruit of a hard-fought agreement between Beijing and Washington under Barack Obama's leadership.

The Paris Agreement commits signatories to efforts to reduce greenhouse gas emissions that cause global warming, which is blamed for melting ice caps and glaciers, rising sea levels and an increase in extreme weather events.

They vowed to take steps to keep the worldwide rise in temperatures "well below" two degrees Celsius (3.6 degrees Fahrenheit) from pre-industrial times and to "pursue efforts" to hold the increase under 1.5 degrees Celsius. (**)