Nambiar will later visit Maungdaw -- on the border with Bangladesh -- where the latest spate of unrest began on Friday.
"We're here to observe and assess how we can continue to provide support to Rakhine," Ashok Nigam, UN resident and humanitarian coordinator, told AFP.
The UN has evacuated most of its foreign staff from Maungdaw, which is its main base in the state and has a large population of stateless Rohingya Muslims.
Around 25 people have been killed and a further 41 people were wounded in five days of unrest, an official said.
That death toll does not include 10 Muslims who were killed on June 3 by a Buddhist mob in apparent revenge for the rape and murder of a woman, which sparked the violence in Rakhine.
Hundreds of Rohingya, many of them women and children, have attempted to flee to Bangladesh in rickety boats but have been turned away by border guards.