Suspected jihadists have massacred at least 138 civilians in Burkina Faso's volatile north in the deadliest attacks since Islamist violence erupted in the West African country in 2015, officials said Saturday.

President Roch Marc Christian Kabore denounced an attack near the borders with Mali and Niger, where jihadists linked to Al-Qaeda and Islamic State have been targeting civilians and soldiers.

"Several injured have succumbed to their wounds and new bodies have been discovered. The still provisional toll is 138 deaths," one local official said Saturday evening.

"The bodies were buried in mass graves," the official said, adding that "there are dozens of injured" after the overnight attack by armed assailants.

"We must remain united and solid against these obscurantist forces," Kabore said, condemning the massacre in the village of Solhan as "barbaric" and "despicable."

Declaring three days of national mourning, ending Monday night at 11:59 pm, the government stated that "terrorists," a term for jihadists, killed civilians of all ages and set fire to homes and the main market.

A security source lamented "the heavy human toll, the worst recorded to date," while warning it could still increase.

Meanwhile, United Nations chief Antonio Guterres' spokesman said that he was "outraged" over the massacre.

Guterres "strongly condemns the heinous attack and underscores the urgent need for the international community to redouble support to Member States in the fight against violent extremism and its unacceptable human toll," Stephane Dujarric said in a statement, offering Burkinabe authorities the UN's "full support".

The assailants struck around 2:00 am (0200 GMT) against a position of the Volunteers for the Defence of the Motherland (VDP), an anti-jihadist civilian defence force which backs the national army, before attacking homes and carrying out "executions," a local source said.

Opposition leader Eddie Komboigo demanded that "the massacre of our people, we never tire of repeating, must stop unconditionally. Every measure must be taken to protect the Burkinabe" people.

The VDP was set up in December 2019 to help Burkina's poorly-equipped military fight jihadists but it has suffered more than 200 fatalities, according to an AFP tally.

The volunteers are given two weeks' military training before working alongside the security forces, typically carrying out surveillance, information-gathering or escort duties.

- 'Neutralise these terrorists' -

The government said that "the defence and security forces are at work to neutralise these terrorists and restore calm to populated areas."

A security forces official said that men were deployed to secure populated areas and to remove and bury bodies.

Solhan, a small community around 15 kilometres from Sebba, the main city in Yagha province, has suffered numerous attacks in recent years.

On May 14, Defence Minister Cheriff Sy and military top brass visited Sebba to assure people that life had returned to normal, following a number of military operations.

The massive attack by suspected jihadists came hours after another attack Friday evening on Tadaryat village in the same region in which 14 people were killed, including an armed volunteer who had come to help them.

Since 2015, Burkina Faso has struggled to fight back against increasingly frequent and deadly jihadist attacks from groups including the Group to Support Islam and Muslims (GSIM) and the Islamic State in the Greater Sahara (EIGS).

The attacks first started in the north near the Mali border, but have since spread to other regions, particularly in the east.

Around 1,400 people have died and more than a million have fled their homes.