KOMSILGA COMMUNE, Burkina Faso — A wave of violent attacks and suspected terrorist activity in Burkina Faso has triggered a sudden humanitarian crisis, uprooting hundreds of thousands of people from their homes in what was once one of West Africa’s most tranquil nations.

In the space of just three weeks , the number of internally displaced people in Burkina Faso has increased by almost 70 percent to nearly half a million people, in a nation of 20 million, according to the United Nations refugee agency . About one-third of the country’s territory has become engulfed in fighting between armed groups, making the area inaccessible to aid workers, UNICEF officials said.

“The attackers came into our village, they killed my husband and they left. They claimed nothing and left us with orphans,” said Mariam Birba, 32, who arrived earlier this month at a roadside camp for internally displaced people, about 12 miles south of the capital, Ouagadougou.

Ms. Birba and four other residents from the village of Pissélé, less than 100 miles north of the capital, said that on the evening of Sept. 21, about 40 men wielding Kalashnikov rifles and riding motorbikes came screeching to a halt and opened fire, killing eight people. Survivors said that they didn’t know who the attackers were or where they came from, but the attackers warned the villagers that they had 48 hours to leave their homes or face more violence .