By Tiemoko Diallo

BAMAKO, May 3 (Reuters) - Mali's army said it killed four Tuareg rebels after they attacked a military convoy on Saturday in the desert north in the first clash since a ceasefire was agreed a month ago, a Malian military officer said.

The April 3 ceasefire agreed in Tripoli, Libya had produced a lull in months of sporadic attacks by the rebels, who had been seeking to control trading routes through which everything from cigarettes and cocaine to small arms and migrants are smuggled.

The Malian military source, who asked not to be named, said an army resupply convoy came under attack on Saturday 50 km (30 miles) from Tessalit, in Mali's desert Kidal region which borders with Algeria to the north.

"Our men fought back and the rebels left four dead on the field, although we don't know if there are other dead," said the officer, who did not mention any government casualties.

He added the attackers were believed to be a group of insurgent Tuareg fighters from Tessalit.

The main rebel group led by insurgent leader Ibrahim Ag Bahanga this week released three of 33 captured army soldiers they were holding hostage. The Tripoli deal had foreseen the rebels freeing all hostages and the army withdrawing partially from positions around the desert trading town of Kidal.

After last month's truce brokered by Libya, the Malian army had kept its troops on a war footing in the north because it did not trust the rebel's pledge to respect the ceasefire.

Mali's eastern neighbour Niger faces its own Tuareg-led revolt which has killed over 70 government soldiers in barely a year, mainly in attacks near its northern uranium mining zone.

Fiercely proud of their independence from outsiders, the Tuaregs staged revolts in Mali in the 1960s and 1990s and in Niger in the 1990s for more autonomy from black African-dominated governments in capitals more than 1,000 km (600 miles) away.

Peace agreements after the 1990s rebellions aimed to grant Tuareg communities a greater degree of autonomy while at the same time integrating former fighters into the national army and promoting Tuareg politicians. But grievances have resurfaced. (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/) (Editing by Pascal Fletcher)

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