Rebels have attacked a refugee camp in Chad, home to some 17,000 people from neighbouring Sudan, UN officials say.
Chad has 12 camps hosting Sudanese refugees from Darfur
One security officer was killed in the attack near the border village of Koukou, the UN refugee agency said.
Earlier, the government said it had beaten off Sunday's rebel attack on a military garrison in southern Chad.
The BBC's Stephanie Hancock in N'Djamena says security in the country is deteriorating ahead of presidential elections scheduled for next month.
Rebels claimed responsibility for the garrison attack and our correspondent says it is believed the United Front for Democratic Change (FUCD) rebels are behind this attack too.
A large number of army officers have deserted to join the FUCD, a coalition of rebel groups led by Mahamat Nour from bases in Darfur on Sudan's border with Chad.
Our correspondent says the camp attacked is the most southerly of the 12 border camps housing some 200,000 Sudanese refugees who fled fighting in Sudan's western region of Darfur that erupted early in 2003.
Rebels arrived at 1600 local time and exchanged fire with security officers protecting the camp. One guard died and two others were injured.
They entered the camp when food was being distributed, the UNHCR said.
Chad's government is refusing to call the attackers rebels and blames Sudan for the two incidents.
Chad says the assailants were mercenaries supported by Khartoum.
"It's little groups - bandits, mercenaries - under the command of the Sudanese government, who've come to disrupt our election campaign, nothing more, nothing less," Chad's Territorial Administration Minister Mahamat Ali Abdallah told the BBC.
Sudan has repeatedly denied such allegations.
In December, Chad declared a state of war with Sudan following a deadly attack launched from Darfur by Chadian rebels.
Earlier this year, Chad and Sudan signed an accord to resolve their differences over fighting along the border.
"Once again we are asking the regime of Khartoum to let Chad live, because its objective is to destabilise Chad," Mr Ali Abdallah said.
The garrison attack at Haraze-Mangueigne "was vigorously repelled" and the camp remained under the total control of the government, he said.
Speaking to Reuters news agency a FUCD rebel spokesman, Abdullahi Abdel Karim, said their forces had withdrawn from Haraze-Mangueigne, near the border with the Central African Republic for "strategic reasons".
"The final objective is to take N'Djamena before the elections," he said.
The FUCD is seeking to overthrow President Idriss Deby, who seized power in 1990 after launching a rebellion from bases in Darfur.
The president is standing for re-election in May, but the main opposition parties say they are boycotting the vote.