Rights groups say Rohingya Muslims have fled religious persecution
An American medical charity has warned that thousands of Burmese refugees in Bangladesh are facing starvation.
Physicians for Human Rights said government authorities are preventing the Rohingya, a Muslim minority, from receiving adequate care.
It accuses Bangladesh of obstructing efforts to help the Rohingya, who have fled Burma to escape persecution.
The government has dismissed the allegations as it did similar reports by MSF last month.
The new report by the Physicians for Human Rights, "Stateless and Starving: Persecuted Rohingya Flee Burma and Starve in Bangladesh," says children will starve if aid is not allowed to be delivered.
It blamed the Bangladesh authorities for "arbitrary arrests, illegal expulsion and forced internment" of Burmese refugees, as neighbouring Burma prepares for elections later this year.
The report described the makeshift camps for unregistered refugees - where an estimated 200,000 Rohingya are living - as "open-air prisons".
"The government of Bangladesh is absolutely ignoring it. They are sweeping it under the rug," said Richard Sollom, director of research and investigation for the group.
Many Rohingya fled Burma last year and were caught by the Thai army
"Basically, it's the policy of the government that they simply want [the refugees] to disappear," he said.
Abdul Momen, Bangladesh's representative in the United Nations, said this was "totally false".
"Government officials just have to make sure that any aid isn't coming from terrorist groups," he said.
"We are the victims. The Burmese people have been kicked out of their country and we gave them shelter.
"We are an impoverished country, and in spite of that, we tried to help them as best we can."
Apart from one or two "sporadic incidents" he denied that there was widespread abuse.
Bangladeshi Foreign Minister Dipu Moni said that claims of abuse were baseless and malicious and she asked the international media to stop reporting them.
She also called for the UN to send the Rohingya back to Burma as soon as possible.
The BBC's Mark Dummett, in Bangladesh, reports that life must be dreadful in Burma for these people to choose to stay in Bangladesh - one of Asia's poorest countries.
Last month, another medical aid group, Medecins Sans Frontieres, also warned of a humanitarian crisis unfolding in a squatter camp where a growing number of Rohingya refugees now live.
Another report, released by the Arakan Project, a Bangkok-based lobby group, made similar claims.
UK-based aid group Islamic Relief Worldwide pulled out of Bangladesh last month because the government did not permit them to work with nearly 13,000 unregistered Rohingyas in the south.
The Rohingyas are Muslims from north-west Burma who speak a dialect of Bengali.
They are among the world's least wanted and most persecuted people.
Burma denies them citizenship and refuses to let them own land. It does not allow them to travel or marry without first seeking permission.