A car bomb has exploded in the northern Mali town of Kidal, killing seven people, reports say.
The attack is thought to have targeted a checkpoint manned by a Tuareg group which has come out in support of France's military intervention.
Islamist militants were driven out of Kidal and other strongholds but have continued to stage raids and bombings.
A senior UN humanitarian official has said hundreds of thousands of displaced Malians are too afraid to return home.
More than 430,000 people who fled the militant takeover of northern Mali last year did not feel confident enough to return to their homes despite the security situation improving, said John Ging, from the UN Office for the Co-ordination of Humanitarian Affairs.
Those who had stayed feared the conflict was not yet behind them, he added, amid reports of amputations and rape carried out by militants against women and children.
There were also fears among ethnic Tuaregs of reprisal attacks by Malian security forces, because Tuareg rebels took part in last year's rebellion before it was hijacked by Islamist militants, the UN official said.
The army has been accused of carrying out extra-judicial killings in areas where it has regained control.
Mr Ging said he had told Mali's government it should show it could protect civilians and secure cities in order for people to feel safe enough to come back.
Tuesday's powerful car bomb exploded at a checkpoint in Kidal belonging to the secular Tuareg MNLA.
A statement from the group said seven MNLA fighters had been killed as well as a suicide bomber.
The MNLA was originally allied with Mali's militant Islamist groups when they seized control of northern Mali in April 2012 but it later fell out with them and backed the French-led offensive to drive them out.
When French troops seized Kidal's airport a month ago, the MNLA took control of the town itself. Chadian troops have also moved into the area.
Two people died in car bomb attacks in Kidal last week. The town is close to the Ifoghas mountains, where members of al-Qaeda in the Islamic Maghreb (AQIM) are thought to be hiding.
Clashes in the area, close to the Algerian border, led to the deaths of 13 Chadian soldiers and dozens of militants at the end of last week, the Chadian army said.
In a separate development, a document left by AQIM in northern Mali has indicated that disagreements between the Islamists may have led to their defeat.
The document, found by journalists in Timbuktu and published by a French newspaper, is said to contain advice by the head of al-Qaeda in the Islamic Maghreb (AQIM), Abdel Malek Droukdel.
In it, the AQIM leader criticised the Mali militants for implementing Islamic law too quickly and predicted France's intervention.
France - the former colonial power in Mali - launched a military operation last month after the militants appeared to be threatening the south.