UK Prime Minister Boris Johnson will announce tougher climate targets by committing to slash carbon emissions by 78 percent by 2035, almost 15 years earlier than previously planned. 

If confirmed, it will be one of the most ambitious environmental targets set out by a developed nation.

Johnson is set to make the commitment this week ahead of a U.S. climate summit hosted by U.S. President Joe Biden in Washington and before the UK hosts the United Nations Climate Change Conference, COP26, in November, a person familiar with the situation said.

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The Financial Times said emissions from international aviation and shipping were likely to be included in the target.

"We will set our ambition for Carbon Budget 6 shortly, taking into account the latest advice from the Climate Change Committee," a spokesperson for the business department said.

Britain's education secretary Gavin Williamson told Sky News that Johnson had always been clear that the country would be a global leader in cutting emissions.

"We were the first country to enshrine in law our commitment to getting to net zero," he said. "We recognize there are significant challenges with that and there's going to be significant investment."

In 2019, the UK set a net zero greenhouse gas emission target in line with the 2015 Paris climate agreement, which called on countries to take steps to keep the global temperature rise as close to 1.5 degrees Celsius as possible.

The opposition Labour Party and environmental campaign groups welcomed the ambition, but said the move was undermined by a lack of policies to deliver it.

Ed Miliband, Labour's business spokesman, said the government needed to match "rhetoric with reality" and provide decisive action.

Caroline Lucas, parliament's only lawmaker from the Green Party, said the government now needed to cancel road building plans and leave fossil fuels in the ground.

On Monday, Lucas, along with the leaders of six minor parties in the House of Commons, including the Liberal Democrats, the SNP and Plaid Cymru, accused Johnson of "lack of truthfulness" in parliament on a number of issues, including a statement he made in February last year about the UK's CO2 emission reductions.

Johnson had said during Prime Minister's Questions, that the UK had cut CO2 emissions in the country by 42 percent since 2010, on 1990 levels. But the party leader's penned in a letter to the house Speaker that "the reality is the decline of about 38 percent in CO2 emissions has happened since 1990, not 2010."