Allied Democratic Forces rebels with machetes and guns have killed at least 61 civilians at a funeral in east Congo, officials said on Tuesday, in one of the deadliest attacks by the Islamic State-linked group in recent months.

The militants, also known as Islamic State Central Africa Province (ISCAP), claimed responsibility for Monday's attack and said they had killed nearly 100 Christians, according to the U.S.-based SITE Intelligence Group, which monitors militant activities.

The SITE report also said some 30 houses had been set on fire in the attack targeting the funeral ceremony in Ntoyo village in the Lubero territory of Congo's North Kivu.

Macaire Sivikunula, a local administrator, said 61 bodies had been counted so far.

"The victims were caught off guard at a mourning ceremony in the village of Ntoyo at around 9 p.m., and most of them were killed with machetes," he said.

Authorities told Reuters later on Tuesday that 18 people had been killed in a separate suspected ADF attack on another village.

The ADF started as a rebel force in Uganda but has been based in the forests of neighbouring Congo since the late 1990s, and is recognised by Islamic State as an affiliate.

A recent flurry of attacks claimed by the ADF has exacerbated insecurity in east Congo, a mineral-rich region where Rwandan-backed M23 rebels staged a major advance this year, prompting U.S. President Donald Trump's administration to try to broker peace.

Last month the ADF killed more than 50 civilians in multiple attacks, while an ADF attack in July on a church left 38 dead.

MISSING

Colonel Alain Kiwewa, the military administrator for Lubero, said Monday night's death toll could rise as there were still people missing.

As well as using machetes, the assailants also shot dead some victims and set fire to vehicles, said Samuel Kagheni, a local civil society leader.

Alain Kahindo Kinama, a resident, said Congolese soldiers had arrived at the scene on Tuesday morning and that many people were trying to leave the area.

Congolese army spokesperson Lieutenant Marc Elongo said ADF militants had "already committed the massacre" by the time soldiers intervened.

Congo's army and its ally Uganda say they have intensified operations against the ADF in recent weeks.