Celebrations for Madagascar's national day were violently brought to a halt by a deadly grenade attack which claimed the lives of at least two people, police said on Sunday.

A 16-year-old and an 18-year-old were reportedly killed and 84 others have been injured in the capital Antananarivo, according to the gendarmerie.

Madagascar's President Hery Rajaonarimampianina blamed the attack on tensions with political opponents.

"There may be differences of opinion between us, but these acts of destabilization are unacceptable," he said in a broadcast on national television, calling the attack "not just a destabilizing act but an act of terrorism."

Asking for calm, he added: "We will not respond to violence with violence."

No responsibility claim

No group has yet to come forward to claim responsibility for the attack.

The explosion took place around 7:00 p.m. local time (16:00 UTC) during a free concert at the Mahamasina municipal stadium to mark Madagascar's 56th anniversary of independence from France.

Investigators found the remains of a grenade, senior police representative Anthony Rakotoarison said, adding: "Whoever did this wanted to cause great harm."

The last attack to strike Madagascar was in January 2014 when a grenade blast at the same stadium killed a toddler and injured several other people.

No arrests were made in connection with the 2014 blast and no one claimed responsibility.

The Indian Ocean island nation, one of the world's poorest countries, is slowly starting to recover economically after a long period of political instability triggered by the 2009 ouster of President Marc Ravalomanana.

rs/ jm (AFP, dpa)