Andrew Gilmour, the UN assistant secretary-general for human rights, made the comment after a four-day visit to the Cox's Bazar district in neighbouring Bangladesh, where he met people who have fled from Myanmar recently.

"I don't think we can draw any other conclusion from what I have seen and heard in Cox's Bazar," Gilmour said in a statement.

After Rohingya insurgents attacked 30 police posts and an army base on August 25, Myanmar soldiers and police swept through villages in what the government says was a legitimate operation to root out "terrorists".

Rohingya who sought shelter in Bangladesh have reported rape, killings and arson by security forces. The United Nations and United States have concluded the campaign amounted to ethnic cleansing.

Gilmour spoke to refugees who recounted abductions by security forces and at least one apparent death of a Rohingya man in custody in February, the statement said.

"It appears that widespread and systematic violence against the Rohingya persists," Gilmour said.

"The nature of the violence has changed from the frenzied blood-letting and mass rape of last year to a lower intensity campaign of terror and forced starvation that seems to be designed to drive the remaining Rohingya from their homes and into Bangladesh."

Despite Myanmar saying it was ready to accept back refugees under an pact signed with Bangladesh in November, he added, "Safe, dignified and sustainable returns are, of course, impossible under current conditions".

Myanmar government spokesman Zaw Htay said he had not seen the UN statement published on Tuesday, but that Myanmar was not committing ethnic cleansing.

"We don't drive out the refugees," he said.

'ORDERED TO VACATE'

Separately, the UN refugee agency, UNHCR, said it was concerned about people living just inside Myanmar at its border with Bangladesh.

The office of the United Nations High Comissioner for Refugees is monitoring developments after several thousand people living in a makeshift camp "were reportedly ordered to vacate the area by the Myanmar authorities", the agency said.

Residents of what is called "no-man's land", as it sits outside Myanmar's border fence but on its side of a creek that separates the two countries, say Myanmar officials have warned them on loudspeakers that their presence on the border line is illegal.

"UNHCR underscores that everyone has the right to seek asylum, just as they also have the right to return home when they deem the time and circumstances right," it said in a statement late on Monday.

"People who have fled violence in their country must be granted safety and protection and any decision to return must be voluntary and based upon a free and informed choice."

Zaw Htay said Myanmar had the right to move people from its territory and part of an agreed "buffer zone" with Bangladesh. Authorities had received information that "terrorists" linked to the August attacks on Myanmar's security posts were sheltering there, he added.

"According to procedure security forces have to clear the area for security reasons," he said.

Zaw Htay said he believed the people were staying on the border to "trap" Myanmar into conducting a "clearance operation", which he said media and the United Nations would label as ethnic cleansing.

Bangladesh last week protested to Myanmar's ambassador in Dhaka after Myanmar security personnel, estimated to number more than 200, gathered near the border.

"Troop movements so close to them are making things even worse," said Major Iqbal Ahmed of Bangladesh's border guard. "They are now even more reluctant to go back to their homeland."