ABUJA (Reuters) - The vast majority of almost 2 million Nigerians driven from their homes by the conflict with Boko Haram cannot return because of a lack of security, an aid agency said on Wednesday.

About 1.8 million people have been displaced in Nigeria by the conflict with the Islamist insurgency, which has left at least 20,000 dead and shows little sign of ending as it drags into its ninth year.

The Norwegian Refugee Council (NRC) said in a report that 86 percent of internally displaced people were not ready to return home in the immediate future. Insecurity is cited by 84 percent of them as the main reason for wanting to stay put, it said.

Only about six in 10 people said they wanted to return to their villages at some point, but could not do so now, the NRC report said.

Many of the displaced say they have tried to return home, only to be forced to flee back to safer camps and cities because of continued attacks by Boko Haram and general insecurity.

“While the end game is for communities to return home, the unfortunate truth is that pushing people back now will have harmful consequences,” Jan Egeland, NRC secretary general, said in a statement.

Although Boko Haram in recent months has increased its attacks on displaced people, they still feel safer in camps and urban centers than in their communities, said Egeland.

The Nigerian government and military have repeatedly said the insurgency has been “defeated”.

Despite that, Boko Haram has killed 381 civilians in Nigeria and Cameroon since the beginning of April, more than double the amount dead in the preceding five months, Amnesty International said last month.

The NRC survey did not take into account the roughly 200,000 refugees who have fled to neighboring countries such as Cameroon, Chad and Niger.

The humanitarian crisis in northern Nigeria is now one of the biggest in the world, with $1 billion needed to fund relief efforts in 2017, the United Nations says.