The joint strikes come shortly after the US and Nigeria announced killing a high-profile IS leader. Meanwhile, residents reported a gunmen attack which killed at least 10 in the northwestern Katsina State.

The United States and Nigeria conducted fresh strikes on Sunday against so-called "Islamic State" (IS) jihadists in northeast Nigeria's Borno State, the US military said Monday.

At least 20 jihadists were killed in the weekend strikes, according to the Nigerian military.

The strikes came shortly after another joint operation between the two militaries that killed Abu Bakr al-Mainuki, the deputy leader of the group's local West African "province."

Nigeria's military described Mainuki as the world's "most active terrorist."

His assassination marked the first successful targeting of a senior militant leader by Nigeria's security forces after more than a decade of insurgency by a number of armed groups in the north, including Boko Haram.

What Do We Know about the Weekend Strikes on Jihadists?

The US Africa Command (AFRICOM) said in a statement that "no US or Nigerian forces were harmed" in the weekend strikes, adding that intelligence confirmed the targets were Islamic State militants.

"The removal of these terrorists diminishes the group's capacity to plan attacks that threaten the safety and security of the US and our partners," AFRICOM added.

The raid was the "continuation of coordinated operations against ISIS militants," across Nigeria's restive northeast region, Nigeria's military said, using another name for the jihadist group.

What Is the Security Situation in Nigeria's North?

Nigeria's Muslim and Christian communities are more or less equally split in size among its population.

The country's Muslim-majority north faces double threats from Islamist jihadists as well as criminal gangs which have increasingly become active in the past decade. Victims are often targeted regardless of their faith, according to analysts.

Last year, US President Donald Trump accused Nigerian authorities of not doing enough to protect the country's Christian community.

The comments led to a row with authorities in the West African country, who denied Trump's accusations.

Shortly afterward, the two countries' militaries coordinated an attack on jihadists on Christmas Day and have since worked more closely together.

The US in February sent troops to Nigeria in what was at the time deemed a mostly advisory and training role. But speculation has grown following the weekend strikes and Mainuki's killing over whether cooperation has advanced to active US involvement in the west African country.

Gunmen Kill at Least 10 in Northwestern Nigeria

In a separate incident in northwestern Katsina State, residents said at least 10 people were killed in an attack by gunmen, including women and children.

Gunmen attacked the rural Guga farming community in Bakori Local Government Area on Sunday, burning homes and looting livestock, the Reuters news agency reported.

"Yesterday evening, heavily armed bandits with sophisticated weapons attacked the farming settlements," Reuters quoted Sale Musa, a resident who said he escaped the attack, as saying. "After opening fire, they captured 10 people, including a pregnant woman, and killed all of them."

Musa said the attack occurred when many residents had gone to the nearby Guga market ahead of the Eid al-Adha celebration, leaving the communities vulnerable.

The Muslim feast involves the slaughter of sheep to commemorate God sparing the life of the prophet Ibrahim's son. Communities typically prepare large numbers of sheep and other livestock ahead of the four-day celebration.