JOHANNESBURG (AP) — A grenade exploded in a stadium in Madagascar, killing two people and injuring more than 80 in what authorities describe as a terrorist attack, authorities said Monday.

The attack happened late Sunday in the Mahamasina stadium, where people had gathered for parades and other festivities marking the country's 1960 independence from France.

Some 84 people were wounded in the attack, reported L'Express de Madagascar. A photograph posted on the website of Madagascar's presidential office showed two youths lying on stretchers, with blood stains visible on the floor nearby.

Madagascar's president, Henry Rajaonarimampianina, visited some of the wounded in a hospital and expressed his condolences to the families of the dead. The government promised tough action against those it accuses of using violence for "political reasons."

The Madagascar Tribune described the attack as a "nightmare" and, in an editorial, questioned how an assailant could have smuggled a grenade into the stadium and noted that emergency services were not widely deployed in the area.

Security commanders had addressed the media last week about plans to secure the stadium amid rumors that the celebration might be targeted.

Rajaonarimampianina's election in 2014 came after five years during which Madagascar was led by a regime that seized power in a coup. Despite hopes that his election would bring stability, the president has faced an impeachment attempt in the National Assembly.

The 2009 takeover had prompted international donors to cut aid that accounted for up to 70 percent of the national budget. Investors pulled out of the country. Donors have since resumed direct ties with the government in Madagascar, though the island nation of 23 million off Africa's southeast coast remains one of the poorest in the world.