REPUBLIKA.CO.ID, MOGADISHU -- African Union troops in Somalia have dismissed reports they killed several civilians during fighting, saying those shot were all Al-Qaeda-affiliated Shebab insurgents.

Witnesses in the southern port town of Merka said troops from the 22,000-strong AMISOM force killed at least eight civilians on Tuesday, opening fire after insurgents hurled a grenade at a passing convoy.

"There was a grenade attack targeting the peacekeepers as they passed by... they opened indiscriminate fire killing many civilians, including children and a woman," said resident Abdirahman Mohamed.

Ibrahim Adam, another witness, said he saw the troops storming a house after the explosion.

"Two children and a woman are among the dead, they have shot anyone they saw moving in the area, and all of the victims were civilians," he said.

But the AU force said the only people killed were Shebab fighters.

"AMISOM categorically denounces this devious allegation," the force said in a statement issued late Tuesday.

"As AMISOM is mandated to do, five Shebab fighters were killed including one of their notorious leaders, Mohammed Dahir."

Deployed to Somalia since 2007, AMISOM has helped push back Shebab across much of the country's south, retaking towns and territory the group had held for years.

US drone strikes have also taken their toll on Shebab, killing senior commanders, including the group's leader Ahmed Godane in September.

Under pressure in Somalia, Shebab has stepped up its attacks in neighbouring Kenya.

In September 2013 four Shebab gunmen killed at least 67 people in an assault on the Westgate shopping mall in the capital Nairobi.

In April this year, four Shebab gunmen killed 148 people, most of them students, in an attack on a university in the Kenyan town of Garissa, the group's deadliest attack to date.

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