-This article has been corrected on 26 May: see final paragraph
During Obama's state visit to the UK, the White House and Number 10 websites issued a joint statement saying that VSO and Peace Corps would share best practice in areas such as training and systems, promote volunteering and address development issues such as education, health, and HIV and Aids.
"The partnership between Peace Corps and VSO will leverage the resources of both organisations to improve the lives of poor and marginalised people and to promote the value of volunteering in global development," the statement says.
"Peace Corps and VSO will harness complementary strengths, share knowledge and collaborate on key development interests, building on our nations' shared history of volunteerism."
A VSO spokeswoman said the two organisations already collaborated informally in some countries but would now do so in all 25 countries where they both work.
She said VSO was happy for the announcement to be made by the Prime Minister rather than the charity itself. "Both organisations receive most of our funding from our governments, so we have a responsibility to them as our funders," she said.
Marg Mayne, chief executive of VSO, said the move was a "landmark step forward for VSO and our transatlantic friends".
"Peace Corps and VSO will support each others' efforts to develop volunteer programmes that are more effective in engaging poor communities in shaping their own futures," she said.
Aaron Williams, director of Peace Corps, said: "This innovative partnership will enhance the effectiveness and impact of both Peace Corps and VSO.
"We will share best practice in programming and training, strengthening our united efforts to combat global poverty."
- The story says VSO and Peace Corps will collaborate in the 25 countries where they both work. In fact they will explore ways in which they might collaborate.