Armed men have shot dead a traditional ruler, and kidnapped his wife plus one other person in south-western Nigeria, authorities say.

The attackers stormed the palace of Segun Aremu - a retired army general and monarch whose official title is the Olukoro of Koro - on Thursday night.

It is not clear who the gunmen were or whether they are demanding a ransom.

This latest killing and abduction comes days after campaigners demanded a state of emergency to deal with the issue.

Some 50 civil society groups want President Bola Tinubu to make that declaration, saying more than 1,800 people had been abducted since he took office last May.

But the true number of abductions during that time could be more than double that figure, at almost 4,000 people, says Nigerian risk consultancy SBM Intelligence.

No matter how desperate the circumstances, Nigerian law prohibits the payment of ransom money. However, many victims pay up because they do not trust authorities or their track record.

Condemning the killing of the Olukoro of Koro in Kwara state, as "reckless, shocking, and abominable", Governor AbdulRahman AbdulRazaq has vowed that the authorities would catch those responsible.

Police say a manhunt is underway. They have also promised the local community they will set up a police outpost.

Nigeria is home to hundreds of traditional rulers, who have no constitutional role but are a respected presence in community life. They are often called upon to settle disputes between local people and lead cultural activities.

Spate of kidnappings

Earlier this week, kidnappers seized five schoolchildren and four teachers in nearby Ekiti state, demanding a ransom of 100m naira ($110,000; £87,500) for their release.

A senior government official was kidnapped on Wednesday night in the Bwari suburb of the capital, Abuja, not far from the home of six sisters who were abducted for ransom last month with their father.

One of the girls was shot dead due to a delay in paying the ransom, in a case that prompted public outcry.

Elsewhere, two girls were also recently kidnapped in the Chikakorie area of Kubwa, another suburb of Abuja. Their abductors have demanded about $25,000 for their release.

Kidnapping for ransom has worsened in Nigeria in recent years with armed gangs targeting road travellers, students as well as residents in rural and urban areas across the country.