U.S. President Barack Obama boards Air Force One | Ashley Landis/WPA Pool/Getty Images Obama to visit UK to argue against Brexit US president’s intervention infuriates Leave campaigners.

U.S. President Barack Obama will head to London in April and will urge U.K. voters to choose to stay in the European Union, according to the Independent on Sunday.

Obama has previously said he wants Britain to remain in the EU to help maintain the two countries' post-war transatlantic partnership. Rumors have circulated for months that he was planning “a big, public reach-out” before the referendum in June to persuade British voters of the merits of staying in the EU.

The president's intervention will be a major coup for the In campaign, as he is considered "the greatest electoral campaigner of his generation," according to the newspaper.

Tim Farron, leader of the pro-EU Liberal Democrats, said Obama’s visit was “welcome.” He added: “This is a reminder that if Britain wants to be a big player on the world stage, then being in the EU is one of the ways we achieve it."

George Osborne, the chancellor of the exchequer, also expressed his support for the In campaign Sunday. In an interview on the BBC's Andrew Marr show, he said: "An exit from the European Union would create an economic shock, increase prices and damage living conditions."

"I am not for pulling up the drawbridge ... Let's not withdraw from the rest of the world."

But Leave campaigners are said to be furious at the prospect of the president swaying undecided British voters. An online petition already has almost 16,000 signatories, who want to “stop President Obama from speaking inside our Westminster Parliament concerning Britain staying inside the European Union.”

Steve Baker, a Conservative MP, told the Independent on Sunday: “Whenever a U.S. president intervenes in our constitutional future, I always reread the U.S. Declaration of Independence. We will solve peacefully at the ballot box the problem for which their nation fought a bloody war of insurrection."

The White House has yet to confirm Obama's visit to the U.K.