Speaking to reporters following a visit to refugee camps in Bangladesh's Cox's Bazar on Friday, Mark Lowcock, the United Nations under-secretary-general for humanitarian affairs, said the body was seeking to raise nearly a billion dollars to help the Rohingya refugees and their host community.
More than 700,000 members of the persecuted minority fled Myanmar following a brutal military crackdown in response to attacks by a Rohingya armed group.
More than 1.2 million now live in overcrowded and squalid refugee camps in southeastern Bangladesh.
Lowcock said the "great exodus" of Rohingya refugees arriving to Cox's Bazar "caused all sorts of issues".
"Our main message is to the wider world: do not forget the Rohingya, do not forget the generosity of the people and institutions and government of Bangladesh, and be generous in supporting both the Rohingya and Bangladesh," he said.
Filippo Grandi, UN High Commissioner for Refugees, who accompanied Lowcock, said the Rohingya refugee crisis should not turn into a "forgotten crisis".
"This remains one of the world's biggest refugee crises," said Grandi.
"I saw a great deal of progress, but their situation, especially for women and children, remains fragile. With the current crisis almost two years on we must give refugees the chance to learn, build skills and contribute to their communities while also preparing for reintegration when they can return to Myanmar," he added.
"It's very clear: nobody has gone back because many of those reasons that pushed them out of the country have not yet been addressed."
Monsoon season
The officials also highlighted the need for stronger infrastructure in the camps in the upcoming cyclone period.
AK Abdul Momen, Bangladesh's foreign minister, who met with the UN officials, reiterated his government's plan to move some 100,000 refugees to to the remote island of Bhasan Char, a move opposed by many refugees.
"We have information that this year there may be more rain and that may cause landslides," Momen told reporters.
"Bhasan Char island is now prepared and we can start to relocate Rohingya before the monsoon to avert any casualties in the coming monsoon," he said.
Some human rights groups have expressed concerns over that plan because the island is remote and prone to devastation from cyclones.
Separately, the International Crisis Group said criminal gangs and fighters were now operating openly in the Rohingya refugee camps, committing killings and abductions with "impunity".
The conflict research group, in a new report on Thursday, called for Bangladesh to toughen its police presence.
Threats from fighters from the Arakan Rohingya Salvation Army, whose attacks triggered the Myanmar military campaign, had left Rohingya leaders fearful for their lives and that frequent murders were "rarely" investigated, according to the ICG.
"Refugees express serious concerns about their personal security, and militants and gangs are intimidating, kidnapping and killing with impunity," the report said.
"Murders and other forms of violence are an almost nightly occurrence... and perpetrators have almost never been brought to justice."