Aid groups and the government of the West African nation have been at a loss to respond to a fast-moving emergency, set off by lawlessness and suspected terrorist attacks in a once-tranquil country.

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.

Such attacks have turned life upside down in Burkina Faso, which until recently had a reputation for its calm, its bustling art scene and its music culture, a contrast to neighboring countries like Mali and Niger, which have been rocked by terrorism and violence in recent years.

The crisis has overwhelmed the local authorities and international aid workers in the small, landlocked nation, where even in more peaceful times, 45 percent of the population lived on less than $1.25 per day. In response to the emergency, only one-third of the requested $187 million in international aid has been fulfilled, according to the United Nations.

“We looked to escape death. There was no time to take anything. We just left like that,” said Kirakoya Adjaratou, 28, another resident of Pissélé, who broke into tears as she recounted the death of the eight men in her village.

While terrorist groups like the Islamic State in the Greater Sahara and Ansaroul Islam are active in the north of Burkina Faso, much of the violence carried out in the country has gone unclaimed. Experts say that personal disputes, ethnic tensions or intercommunal conflicts are often behind the attacks — and not terrorist activity.

“Many of the attacks in Burkina Faso are rarely claimed by terrorist groups. We are, therefore, entitled to ask ourselves who officially is behind terrorist acts,” said Jacob Yarabatioula, a researcher specializing in terrorism at the University of Ouagadougou. “Attacks tend to be linked to community conflicts or settling scores.”

Several military outposts in the northern Sahel region have been abandoned after being attacked by armed men, according to two government officials and an international security adviser, who were unwilling to be identified because of sensitivities related to the deteriorating security situation. Capt. Aziz Ouedraogo, a spokesman for the armed forces in Burkina Faso, declined to comment on reports of military outposts being abandoned.

The violence has been moving south, from the border with Mali, toward the city of Kaya, which is about 60 miles northeast of the capital.

Most embassies in the country now advise their citizens not to leave the capital. Meanwhile, life in Ouagadougou goes on seamlessly — Muslims attend evening prayers, Christians go to church on Sundays and the city’s young people sip on cold Brakina beers at popular restaurants late into the night. But that sense of normality is slowing being eroded by a foreboding feeling of crisis edging toward the capital.

People here vividly remember the attack in August 2017 on the Aziz Istanbul restaurant in Ouagadougou, which killed 19 people, including nine foreigners. In 2016, a terrorist attack targeted a hotel and restaurant in the capital, killing 30 people.

Between Aug. 6 and Sept. 30 of this year, at least 26 military personnel from Burkina Faso’s armed forces were killed and 25 were injured in attacks, according to figures compiled by international organizations working in the country.

On Friday, at least 15 people were killed when gunmen attacked a mosque in Oudalan Province, close to the border with Mali, a local security official confirmed, speaking on the condition of anonymity as he was not authorized to speak publicly.

The attack took place in the north of the country, where an Islamist insurgency led by armed groups with links to Islamic State and Al Qaeda are present.

Ioli Kimyaci, the head of the United Nation’s refugee agency in Burkina Faso, said in an interview that in addition to the nearly half a million internally displaced people, another 16,000 have asked for asylum in neighboring countries since 2018. Some 12,000 of them went to Mali.

“Everything is saturated. The absorption capacity of the host communities has reached its limit,” she said.

The United Nations is now looking to open new camps in Burkina Faso because of overcrowding at sites in the north, around the city of Dori. Tents designed for a family of seven are sometimes being used by up to 50 people, Ms. Kimyaci said.

“It’s true that the situation has overwhelmed us,” said Emilie Fernandes, the director for Save the Children in Burkina Faso.