"The UN refugee agency has first-hand, credible accounts of boats from Myanmar not being enabled to access Bangladeshi territory. These reports indicate women, children and some wounded are onboard," the agency said in a statement.
Andrej Mahecic, spokesman of the U.N. High Commissioner for Refugees (UNHCR), told a news briefing in Geneva: "They are turning them back. Some were quite close because the locals were trying to give assistance to them."
Those adrift are in desperate need of water food and medical care, he said, adding: "We have been talking to the Bangladeshi authorities and we hope that Bangladesh, in line with its long tradition of hospitality for the people of Myanmar, will allow access to safe haven and to assistance for this people."
There are already some 30,000 Rohingyas staying in two camps in Cox's Bazaar, Bangladesh.
Tens of thousands of displaced Muslim Rohingyas and ethnic Rakhine Buddhists were in need of food, water and shelter in northwestern Myanmar on Thursday after fleeing the country's worst sectarian clashes in years.
U.N. officials who reached Rakhine this week saw a number of "smouldering villages" in the border areas affected by the recent riots, the UNHCR said.
"Based on what we saw, we consider that displacement could be considerable. The government estimates that some 30,000 people have been displaced," Mahecic said.