The sources said a Malian army convoy, backed by helicopter gunships, was trying to break through rebel positions and bring supplies and reinforcement to a besieged military base about 7 km (4.3 miles) outside Tessalit when they came under attack.
“What can be said is that there has been more than 100 dead, (on the rebel side) and 50 were taken as prisoners,” one of the sources, a senior military officer at the Malian defence ministry said on condition of anononymity.
The officer said more than 30 rebel vehicles were destroyed while the army, which was using mainly helicopters in the combat, suffered two losses.
Dozens have been reported killed and thousands of civilians forced from their homes since the MNLA rebels, who say they are fighting to create an independent north, boosted by ethnic allies who returned to Mali after fighting for Muammar Gaddafi in Libya, started attacking towns and army bases last month.
Moussa Ag Acharatoumane, a spokesman for the rebels, confirmed that fierce combats had taken place near Tessalit but denied their fighters had suffered any losses.
“There was some violent clashes near Tessalit as a convoy of the Malian army was trying to reach Tessalit from Kidal but which was intercepted by our men. They tried again through another route but we stopped them,” said Acharatoumane.
“So effectively, there was some violent fighting but we did not record any death, just about 3 wounded,” he said by telephone from Europe.
Another military source at the Malian defence ministry said the death toll was more than 100 on the rebel side, with another 100 taken prisoners while 30 rebel vehicles were destroyed.
It is has so far been difficult to independently verify the casualty figures.
Mali will be seeking the backing of regional leaders of the Economic Community of West African States who began meeting in Nigeria on Thursday, with the situation in northern Mali as one of the items on their agenda, a Malian diplomatic source said.