Obama pays tribute to slain British MP Jo Cox

US President Barack Obama on Wednesday offered a heartfelt tribute to murdered British MP Jo Cox, hailing the "remarkable life" of a woman who volunteered on his campaign in 2008.

"Jo knew that our politics, at its best, still works — that, if we recognise our humanity in each other, we can advance the social justice, human dignity and peace that we seek in the world," Obama said in a tribute published on Facebook.

While Obama never met Cox, who would have been 42 on Wednesday, he explained that she had come to America to volunteer on his first White House campaign.

"She gave her time and passion to a country that was not her own because she believed in an idea that transcends borders and cultures — the power of people to bring about change, from the grassroots up," he said.

Obama's comments came on the eve of Britain's vote on whether to stay in the European Union.

The murder of Cox, who was campaigning for Britain to remain in the bloc and was a major advocate for refugee rights, shook the referendum campaign and sent shock waves around the world.

"Today, we stand united — British, Americans and people around the world — to affirm that the hate and violence that took her from us are ultimately no match for the love and compassion that she spread in her life," Obama said.

On Friday, Obama called Cox's husband Brendan to express his condolences over her death, which took place in broad daylight on Thursday in her constituency in northern England.