US officials have cast doubt on reports that Ugandan rebel leader Joseph Kony is negotiating his surrender in the Central African Republic.

CAR officials have said that Kony, wanted for war crimes by the International Criminal Court, has been in talks with their government.

A US State Department official told the BBC that some rebels had been in contact but Kony was not among them.

The US has offered up to $5m (£3.3m) for leads resulting in his arrest.

Kony founded the Lord's Resistance Army in northern Uganda more than 20 years ago, and his fighters are notorious for abducting children to serve as sex slaves and child soldiers.

The US official also noted that Kony had previously used "any and every pre-text to rest, regroup, and rearm, ultimately returning to kidnapping, killing, displacing and otherwise abusing civilian populations".

The LRA was forced out of Uganda in 2005 and since then has wreaked havoc in CAR, South Sudan and the Democratic Republic of Congo.

Kony was on the verge of signing a peace deal in 2008 but insisted that the ICC first drop its arrest warrant, which it refused to do.

On Wednesday, a CAR government spokesman told the BBC that Kony was in the country but wanted his security to be guaranteed before giving himself up.

The State Department official said the United States was aware that CAR authorities "have been in contact for several months with a small LRA group in CAR that has expressed interest in surrendering".

"At this time, we have little reason to believe that Joseph Kony is part of this group," he said.

Also on Wednesday, the African Union's special envoy on the LRA, Francisco Madeira, told the UN Security Council he had seen reports that Kony was suffering from a "serious, uncharacterised illness".

In April, the Ugandan army suspended a search for Kony in the CAR, blaming "hostility" from the government formed when rebel forces took power there.

Several thousand African troops, backed by 100 US special forces, have been hunting him and his fighters across the region.

Mr Madeira said the military pressure had kept Kony and the LRA "on the run".

Kony claims the LRA's mission is to install a government in Uganda based on the Biblical Ten Commandments.

But he is wanted by the International Criminal Court on charges of rape, mutilation and murder of civilians, as well as forcibly recruiting children to serve as soldiers and sex slaves.

His global notoriety increased when a US activist group called Invisible Children released a video, Kony 2012, which went viral on the internet and was viewed tens of millions of times across the world.

The highly emotive video profiled Kony and the history of the LRA, but Invisible Children came in for criticism from some for oversimplifying the conflict and for not spending enough of the money raised on the LRA's victims.