GENEVA/LAGOS (Reuters) - A U.N. expert asked Nigeria on Thursday for urgent information about a forced eviction of thousands of people from makeshift homes in Lagos, although the state government denied reports of brutality and possible breaches of human rights laws.

Residents and a rights group said 30,000 people were forced a week ago from bamboo homes built illegally in the city's Lekki neighborhood - a prime site for luxury apartments - in defiance of a court order to wait.

Campaigners and residents told a Reuters reporter at the scene that the demolition had happened after fighting between locals and people from Benin, a nation just west of Lagos.

But in a statement issued late on Thursday, Lagos state government said the shanty town was destroyed by fires set during violence between ethnic groups within the community.

In August, the Lagos state government gave residents who lacked building permits two weeks to move out of Lekki and other upmarket districts. Authorities have since demolished several shanty towns that it says were home to criminal gangs, making them a security threat as well breaching building regulations.

The U.N. special rapporteur on the right to housing, Leilani Farha, said on Thursday that she was told "the evictions may have involved the extreme use of force and fire by the Nigerian police force and Lagos State government" and ignored international human rights guidelines on forced evictions.

"In an urgent communication, Ms. Farha has asked the Nigerian government for information on the evictions, the methods used and their compliance with international human rights law," the U.N said in a statement.

But Lagos state government said it was not responsible for the buildings being knocked down.

"From police reports and evaluation by the government, the waterfront community was razed by the fire incident that happened as a result of the ethic clash," it said.

"While the Otodo Gbame shanties clearly fell within the prime waterfront areas where Lagos state government would prefer to have better development, befitting of a prime area in a mega city, it was mindful of the fundamental rights of the various residents living in the area," it added.

Lagos police last week denied they had destroyed homes and said they had arrested several people for setting fire to them.

Slums of makeshift housing are common in the poorest parts of Lagos, a city of 23 million people, which attracts thousands of people each day in search of work from across Africa's most populous nation and neighboring countries.

(Reporting by Tom Miles in Geneva, Alexis Akwagyiram in Lagos and Felix Onuah in Abuja; Editing by Robin Pomeroy and Catherine Evans)