Her comments followed what she called "horrendous violence" and attacks on civilians in areas bordering Sudan's conflict-riven Darfur region.
"I am deeply concerned that the horrendous violence that has been wracking Darfur is affecting Chad," the UN High Commissioner for Human Rights said in a statement.
"Action must be taken immediately to stop a full-blown human rights crisis in south-eastern Chad," Arbour added.
Armed men on horseback again have attacked, looted and burned several remote villages in south-eastern Chad over the past week, leaving many dead and forcing hundreds to flee their homes, according to the government and relief agencies.
About 300 people have been killed in the violence since late October, they added.
About 180 of those deaths may have occurred in raids over the past week, according to reports received by UN agencies.
"Survivors describe their attackers as Arab nomad tribes, both Chadians and Sudanese," said Ron Redmond, a spokesman for the UN refugee agency.
"The testimonies are harrowing, including reports of babies, children, the elderly and infirm being burned in their houses because they were unable to flee," he told journalists. "In one village seven children were burned alive according to residents."
Arbour urged the government of Chad to protect the civilian population and called on armed groups to stop their attacks.
"It is also the government's duty to bring those responsible for the violence to justice," she said, noting an official announcement on November 8 that the authorities would establish responsibility for the attacks.
Chad's government declared a state of emergency in the region and the capital N'Djamena on November 13.
Arbour called on the government to respect human rights and freedoms during this period, which she hoped would be as short as possible.
The office of the UN High Commissioner for Refugees said that thousands of people were continuing to flee the region, while more Sudanese refugees were arriving there from neighbouring Darfur. There are about 218,000 Sudanese refugees in camps in the region.
"The UNHCR is concerned that there may be combatants among the new arrivals. We have informed the refugees of the humanitarian and civil character of our refugee camps," said Redmond.
The refugee agency has repeated warnings about the situation in eastern Chad in recent weeks and called on November 9 for urgent international action.
UN Security Council Resolution 1706 voted in August called for the deployment of a United Nations presence in Chad, as well as in the Central African Republic.

Copyright AFP (Agence France-Presse), 2006