Burkina Faso was in mourning on Wednesday after a wave of militant attacks with dozens of soldiers killed in the latest incident.
Security sources said on Wednesday that "around a dozen soldiers were killed" in an attack overnight in Hallele in the volatile northern province of Soum.
Seven soldiers also died in simultaneous attacks Tuesday on the northern town of Arbinda and a military base, which lasted several hours and were of a "rare intensity", the army said, while 80 assailants were killed.
The earlier attack also killed 35 civilians, mostly women, leading the government to announce a day of mourning.
Burkina Faso, bordering Mali and Niger, has seen frequent militant attacks which have left hundreds of people dead since the start of 2015 when Islamist extremist violence began to spread across the Sahel region.
"A large group of terrorists simultaneously attacked the military base and the civilian population in Arbinda," the army chief of staff said in a statement.
"This barbaric attack resulted in the deaths of 35 civilian victims, most of them women," President Roch Marc Christian Kabore added on Twitter, which was one of the deadliest assaults in nearly five years of violence.
There was worldwide condemnation of the attack, as well as expressions of support for Burkina Faso.
In his traditional Christmas message, Pope Francis denounced attacks on Christians in Africa and prayed for victims of conflict, natural disasters and disease on the world's poorest continent.
The pontiff urged "comfort to those who are persecuted for their religious faith, especially missionaries and members of the faithful who have been kidnapped, and to the victims of attacks by extremist groups, particularly in Burkina Faso, Mali, Niger and Nigeria".
In Brussels, the head of the European Council Charles Michel tweeted: "Inates in Niger yesterday, Arbinda in Burkina Faso today... Martyr towns, victims of a rampant terrorism that threatens us all. The European Union stands by Africa in its battle against terrorism."
Niger's President Mahamadou Issoufou also expressed his "solidarity" and, speaking "in the name of the Nigerien people" offered his "condolences for all civilian and military victims."
The morning raid in Burkina was carried out by more than 200 militants on motorbikes, triggering a fierce firefight that lasted about three hours before armed forces backed by the air force drove the militants back, a security source said.
No group immediately claimed responsibility for the bloodshed, but militants violence in Burkina Faso has been blamed on extremists linked to both Al Qaeda and ISIS.
Leaders of the G5 Sahel nations held summit talks in Niger earlier this month, calling for closer cooperation and international support in the battle against the Islamist threat.
Militant violence has spread across the vast Sahel region, especially in Burkina Faso and Niger, having started when armed Islamists revolted in northern Mali in 2012.
The Sahel region of Africa lies to the south of the Sahara Desert and stretches across the breadth of the African continent.
There are 4,500 French troops deployed in the region as well as a 13,000-strong UN peacekeeping force in Mali to fight insurgents, backing up national forces of the G5 – Chad, Burkina Faso, Mali, Mauritania and Niger.
In Burkina Faso, more than 700 people have been killed and around 560,000 internally displaced, according to the United Nations.
Attacks have targeted mostly the north and east of the country, though the capital Ouagadougou has been hit three times.
Prior to Tuesday's attack, Burkina security forces said they had killed around 100 militants in several operations since November.
An ambush on a convoy transporting employees of a Canadian mining company in November killed 37 people.
Attacks have intensified this year as the under-equipped, poorly trained Burkina Faso army struggles to contain the Islamist militancy.
