"The United States will continue to pressure Myanmar to create necessary conditions for the safe and voluntary return of the Rohingya people to their homeland", he said in the letter.
Members of the United Nations Security Council have told Myanmar's leaders there must be a "proper investigation" into a military crackdown in Rakhine State last August, which displaced nearly 700,000 Rohingya Muslims to Bangladesh.
State television showed the ambassadors touring the border area.
From Sittwe, capital of the Rakhine state, the team flew by helicopter to visit two villages, one transit center and one reception camp, where refugees who return will initially be housed, he said.
They also met with members of different groups affected by the violence, including Rakhine Buddhists, Hindus and some Muslims who did not flee.
Aung San Suu Kyi was helpful and asked the council to share evidence with Myanmar authorities, she said, adding that the Security Council would reflect on how best to respond to the State Counsellor's Office, including an investigation mechanism to provide it with evidence. That investigation led to a United States declaration of genocide and the imposition of economic sanctions against the Sudanese government, the news agency said.
Adams said it's important to note that while the U.N.is doing its job, the U.N. Security Council is a political body made up of governments and that, "they're not doing their job". "The second would be for the Burmese government to do it themselves", she said.
As the largest humanitarian assistance donor in the world, he said, the United States remains committed to supporting Bangladesh alongside "our worldwide partners". Thousands are believed to have died.
On Tuesday, the UNSC members urged the Myanmar government immediate repatriation of thousands of refugees from Bangladesh with the help of United Nations agencies, Myanmar Times reported.
"It is very important to improve the security conditions for the return of the refugees [and] also improve cooperation with global organizations, particularly the United Nations", said Security Council President Gustavo Meza-Cuadra.
"We want to see that happening soon".
The Security Council delegation will hold a press conference on Tuesday evening in Naypyitaw.
"We already have a top-level connection between Myanmar and the USA, to discuss how to solve the Rakhine crisis, including these cases", he said, referring to the alleged atrocities.
An OIC delegation visited the camps in January following the exodus of hundreds of thousands of Rohingya Muslims from Myanmar into Bangladesh after August 25, 2017, when the military and Buddhist mobs torched their homes, wiped out their villages and persecuted them in the northern Rakhine state of Myanmar. Indeed, Suu Kyi has repeatedly denied that rights abuses have taken place, has not criticized the military, and has refused to call the Rohingya.
"We all know that people from Bangladesh's refugee camps can't return home in the short term, so they need to be in the proper shelters during this season", he said.