The United States on Thursday voiced concern over Bangladesh's transfer of Rohingya refugees to a low-lying island and said that any movement should be voluntary.

Bangladesh, which has taken in nearly one million Rohingya who fled a brutal offensive in neighboring Myanmar, has started the relocation of 100,000 of them from squalid camps on the mainland to Bhashan Char, a silt island frequently in the path of cyclones.

The United States reiterated its appreciation to Bangladesh for accepting the refugees but said it was "concerned" about last week's transfer of more than 1,600 Rohingya and plans to move more.

"The United States concurs with the UN that any such relocations must be fully voluntary and based on informed consent without pressure or coercion," State Department spokesman Cale Brown said in a statement.

UN spokesman Stephane Dujarric earlier pointed to reports, corroborated by accounts on the ground to AFP, that refugees have been pressured into relocating. 

Bangladesh's Foreign Minister AK Abdul Momen called the claims "a damn lie" and said facilities on the island were "much better" than the camps.

The United States called for Bangladesh to allow "thorough and independent technical and protection assessments" of Bhashan Char to determine whether the island, said to be prone to flooding, is suitable for refugees.

The US statement comes after outgoing President Donald Trump slashed his country's own refugee admissions to a record low, with the wealthiest nation planning to admit no more than 15,000 from around the world in the current fiscal year.

The State Department said the United States is the leading supporter of refugee programs inside Bangladesh, contributing $962 million since 2017.

The United States also reiterated calls on Myanmar to allow the return of the refugees -- a prospect that few see as immediate.

The Buddhist-majority nation refuses to consider the mostly Muslim Rohingya as citizens and in 2017 launched a military campaign in which refugees recounted mass killings, widespread rape and the burning of villages.