Boris Johnson has told ITV News there is no doubt that "industrial ethnic cleansing" of Rohingya Muslims has been taking place in Myanmar.
More than 620,000 Rohingya have fled to neighbouring Bangladesh since August following persecution from the Burmese military in their native state of Rakhine.
Speaking after visiting Myanmar as part of a four-day trip to Asia, the Foreign Secretary told ITV News correspondent Dan Rivers: "There is no doubt when you fly over northern Rakhine and you look at the scale of the devastation, the industrial ethnic cleansing that has gone on.
"There’s no doubt the military must have been involved.
"What we want to do now is to get those refugees back home in a way that is safe, voluntary and dignified."
The Foreign Secretary said many Rohingya he had met were so in fear of the threat of violence they would not say who burnt down their homes.
“This is a community who have been utterly traumatised, they need to have the confidence and reassurance that when they come back over that border the same purges won’t happen again," Mr Johnson said.
Myanmar's de facto leader Aung San Suu Kyi has faced widespread criticism for her perceived lack of action in dealing with the violence committed against the Rohingya.
On Sunday, Mr Johnson met with Ms Suu Kyi and called on her to help thousands displaced in Bangladesh return to their homes in Rakhine State.
Mr Johnson said the most important thing she can do now is show leadership in getting an international body, such as the UN High Commission for Refugees to oversee that.
Asked if he had encouraged Ms Suu Kyi to act, Mr Johnson said: “Of course, and I think the crucial thing to understand is that she is part of a civilian government whose writ does not entirely run in that country."
He added: “She’s our best hope, she is the democratic face of Burma and of course what we want to see is leadership from her.
"The most important thing she can do now I think is show the world she’s willing to have an international body, preferably the UNHCR, oversee the repatriation of the refugees from Bangladesh into northern Rakhine.
"It’s not going to be easy but it’s got to start happening, because if it doesn’t then it will be clear to the world that ethnic cleansing can take place again in the 21st century and it can be allowed to stand and I think that will be absolutely intolerable."