United Nations (PTI): Expressing "grave concern" over the outbreak of fighting on the outskirts of the Sudanese capital, United Nations Secretary-General Ban Ki-moon has "strongly condemned" the violence and called for an immediate end to the hostilities, fearing it could hamper peace efforts.

Ban's strong condemnation came as Sudanese authorities said that the army had repulsed an unprecedented attack on capital Khartoum by Justice and Equality Movement (JEM), following heavy clashes and the fighting was still going on.

"He condemns strongly the use of armed force and military means by JEM for the achievement of political ends and calls for an immediate cessation of fighting and a renewed commitment to a peaceful resolution of outstanding issues," a UN spokesperson said.

The Secretary-General also expressed his anxiety at the effect they would have on the overall situation in Sudan, as well as on the Comprehensive Peace Agreement and Darfur Agreement and at the possible effect on civilian lives and property of any escalation of such attack.

Sudan blames neighbouring Chad of supporting rebels, a charge Chad denies. Chad said it "unreservedly" condemned the attack.

But this was the daring attack launched by JEM since the Darfur conflict began and diplomats said the main idea was to stress that the rebels had enough strength to bring the fighting to the heart of the country.