The report is based on 81 interviews, 54 of which were conducted on the ground in Rakhine, with people of different ethnicities and religions.
Filippo Grandi said that the government has beeen slow in implementating the human rights procedure in the country.
The new arrivals are from Rakhine Buddhist and other tribal groups, a senior foreign ministry official told AFP on condition of anonymity, without giving a figure.
Amid international call for prosecution, Myanmar to start returning Rohingya in November; Bangladesh agrees
More than 720,000 of Myanmar's stateless Rohingya fled a brutal military crackdown in August last year.
Hindu community leader Jibon Sharma told AFP that the terrifying circumstances of their escape prevented them from celebrating the annual festival last year.
In September last year, India under the 'Operation Insaniyat', extended the first phase of humanitarian assistance comprising 981 metric tonnes of relief supplies.
Life-threatening levels of malnutrition have risen dramatically among Rohingya refugee children who have fled Myanmar for Bangladesh.
More than 500,000 Muslim Rohingya have run from communal bloodshed in Myanmar in the last six weeks and numbers are again rising.