Sudan's armed forces have killed the leader of Darfur's most powerful rebel group, state media said on Sunday, dealing a severe blow to insurgents in the remote western region in their nearly decade-long war with Khartoum.

The Darfur conflict has rumbled on since mainly non-Arab insurgents took up arms in 2003, saying the central government had left them out of the political and economic power structure and was favouring local Arab tribes.

Khalil Ibrahim, head of the Justice and Equality Movement (JEM), emerged as one of the most powerful rebel commanders. In 2008, his group launched a shock attack on Khartoum that killed more than 200 people.

Sudan's authorities have long hunted the leader, who had taken refuge in neighbouring Libya under Muammar Gaddafi until the leader's overthrow deprived him of his safe haven.

Al-Sawarmi Khalid, Sudan's armed forces spokesman, said Ibrahim had been killed early on Sunday morning while trying to cross into South Sudan, which seceded in July under a 2005 peace deal that ended a separate, decades-long civil war.

The armed forces clashed in a direct confrontation with Khalil Ibrahim's rebel forces, and were able to eliminate Khalil Ibrahim, Khalid told state television.

JEM's spokesman could not immediately be reached for comment on Sunday, but Al Jazeera television quoted Ibrahim's brother as confirming the death, saying he died in an air raid on his military convoy.

The death of Ibrahim - often described as commanding and charismatic - could be a major blow to JEM, although tightly restricted access to Sudan's conflict zones has made it hard to gauge the actual strength and internal unity of insurgents.

In November, JEM said it had formed an alliance with other insurgents in Darfur and in two of Sudan's conflict-stricken border states where fighting broke out around the time of South Sudan's secession.

Analysts have questioned how effective the alliance would be, given that Darfur's various rebel factions have rarely been able to sustain long-term military and political coordination.

LIBYAN REFUGE

The United Nations has said as many as 300,000 people may have died in Darfur, where Khartoum mobilised troops and mostly Arab militias to crush the uprising. Khartoum puts the death toll at 10,000.

The International Criminal Court has charged Sudan's President Omar al-Bashir with masterminding genocide and other crimes in the region, a charge Khartoum dismisses as political.

While violence has died down since the mass killings reported in the early days of the conflict, law and order have collapsed and the area has been hit by attacks by bandits, militias, soldiers and tribal groups in recent years.

Various rebel groups, including two factions of the Sudan Liberation Army (SLA), have fought on, even as Qatar brokered a peace deal which Sudan signed with the Liberation and Justice Movement (LJM), an umbrella association of smaller groups.

The major rebel groups, including JEM, have refused to sign the document, dampening hopes the region will soon see peace.

JEM said on Saturday its fighters had clashed with government militias in parts of the North Kordofan state and were planning to advance on the capital Khartoum to overthrow Bashir's government.

(Writing by Alexander Dziadosz; Editing by Jon Hemming)