Violence flared in Rakhine State after a Buddhist woman was raped and murdered by three Muslims.
A series of reprisals and revenge attacks between communities has now left about 50 people dead.
Many of the displaced have sought refuge in Bangladesh, which has now closed its border.
Human rights groups have criticised Bangladesh for the decision, saying it is a violation of international law.
The United Nation's World Food Programme says it has provided emergency food supplies to more than 66,000 people - around two-thirds of those displaced - in the past week.
Poor roads and bridges make reaching many communities difficult, the organisation says.
Two Muslim men convicted of raping and killing the Buddhist woman last month were sentenced to death on Monday.
A third man who died in jail was given a posthumous conviction.
Following the woman's murder in May, a bus carrying Muslims was attacked and 10 people were killed, prompting more unrest in several towns and villages in Rakhine.
Rakhine state is named after the ethnic Rakhine Buddhist majority, but also has a sizeable Muslim population, including the Rohingyas.
The Rohingyas are a Muslim group and are stateless, as Burma considers them to be illegal immigrants from Bangladesh.
The BBC's Jonah Fisher, in Thailand, says there are still reports of sporadic violence but some sort of calm appears to have returned to Rakhine State.
But, our correspondent says, that has not stopped people trying to flee - both internally and across the border to Bangladesh.
Many of those trying to cross to Bangladesh both by land and sea have been turned back, he says.
Bangladesh already hosts several hundred thousand refugees from Burma and says it cannot take any more.
Around 90,000 people have been displaced by fighting in the west of Burma, according to a United Nations body.