YANGON (AFP) - A top United Nations envoy has raised the alarm over "appalling conditions" in west Myanmar displacement camps, which hold thousands of Rohingya Muslims made homeless in communal unrest two years ago.

Some 140,000 people, mainly the stateless Rohingya, are trapped in miserable camps in Rakhine state following violence between Buddhists and Muslims in 2012 that left around 200 dead.

"In Rakhine, I witnessed a level of human suffering in (displacement) camps that I have personally never seen before, with men, women, and children living in appalling conditions with severe restrictions on their freedom of movement, both in camps and isolated villages," said assistant secretary general Kyung-Wha Kang.

The UN official, who visited Myanmar last week, said many people had "wholly inadequate access to basic services including health, education, water and sanitation", in a statement released in Myanmar on Wednesday.

In March, medical aid group Doctors Without Borders (MSF) was expelled from the state, where it provided essential healthcare to hundreds of thousands of Rohingya.

Later that month Buddhist extremists, accusing international aid groups of bias towards Muslims, raided warehouses and destroyed property causing most humanitarian organisations to pull out their staff.

The UN says only 60 percent have been able to return.

Kang, who urged Myanmar to prosecute those behind the violence against aid groups, said hundreds of thousands of people in Rakhine depend on humanitarian help because of restrictions that stop them from fishing, farming and visiting markets.

Myanmar's government refers to the Rohingya as "Bengali" and views many of them as illegal immigrants from Bangladesh.

The UN refugee agency (UNHCR) last week warned of increasing abuse and exploitation for the continuing flood of people fleeing Rakhine.

It estimates more than 86,000 people have left the area by boat from the Bay of Bengal since June 2012, including 15,000 between January and April this year alone.