The measure highlighted the deteriorating security situation in the east of the country, where rebels opposed to Idriss Deby, the president, have stepped up attacks in a campaign to disrupt elections next month.
Deby, who is standing for re-election on May 3, accuses neighbouring Sudan of supporting insurgents from its conflict-torn Darfur region - an allegation that Khartoum denies.
A rebel column temporarily occupied the Chadian village of Koukou Angarana on Monday and the nearby Goz Amir camp housing more than 17,000 refugees from Sudan's Darfur region, about 100km away.
UN officials said one Chadian policeman was killed and three others were injured in the raid on the camp, which is about 50km from the main local town of Goz-Beida.
Matthew Conway, a UNHCR spokesman said: "The United Nations and most NGOs have decided to reduce staff at Goz-Beida ... as a security precaution."
"The United Nations and most NGOs have decided to reduce staff at Goz-Beida ... as a security precaution"
Matthew Conway, UNHCR spokesman
Speaking by telephone from Abeche, 270km to the north of Goz-Beida, Conway said the rebels appeared to have pulled back from both Koukou Angarana and the refugee camp.
"All our offices in the east have checked in and calm is prevailing," he said.
Abdoulaye Abdel Karim, who is a leader of the rebel United Front for Democratic Change, said via satellite phone that they had carried out Monday's raids and the attacks on Sunday against southeastern towns.
"We don't attack refugee camps or humanitarian workers, only government forces," he said.
Diplomats and aid workers said recent rebel statements announcing the capture of large towns in the east - which later turned out to be false or exaggerated - appeared aimed at sowing fear and panic among local officials.
Rebels are trying to topple
The government said it still controlled the country. One diplomat, who asked not to be named, said: "There's a propaganda war being fought here."
Chad's government blamed Sudan for Monday's raid on the refugee camp, which it said caused damage and casualties.
Conway said the agency had received no reports of civilian casualties.
Hourmadji Moussa Doumgor, Chad's information minister, said in a statement: "Sudan has decided to destabilise Chad with carefully planned terrorist strikes."
He referred to the rebels as "mercenaries in the pay of Sudan".
The rebel FUC and other anti-Deby groups say they will step up a military offensive to try to topple him before the election.
"Our objective is N'Djamena [the capital]," Abdel Karim said.