This photo, taken in the Buringa area of Burundi, shows a site flagged by Amnesty International as an "area of interest" in its investigation into mass graves. (AFP/Getty Images)

Satellite images, video footage and witness accounts show that dozens of people allegedly killed by Burundian security forces in December were later buried in mass graves, Amnesty International reported Friday.

The news came as unrest in Burundi escalated with the arrests of 17 people in a security sweep, including two foreign journalists who were released later Friday.

The rights group reported five possible mass graves in Buringa on the outskirts of the capital, Bujumbura, which has been racked by violence as security forces move into neighborhoods seen as opposition strongholds.

Two journalists on assignment for the French newspaper Le Monde were among the 17 people swept up in a military operation Thursday, said Moise Nkurunziza, a spokesman for Burundian police. Jean-Philippe Rémy of France and British photographer Philip Edward Moore were released Friday afternoon, Le Monde said.

France, which had called on Burundian authorities to free the journalists, suspended its security cooperation activities in Burundi late Friday.

Witnesses described how police and local officials scoured Nyakabiga and other neighborhoods in Bujumbura to retrieve the bodies of those who were killed late last year and took them to undisclosed locations, according to Amnesty International.

“The imagery, dating from late December and early January, shows disturbed earth consistent with witness accounts. Witnesses told Amnesty International that the graves were dug on the afternoon of Dec. 11, in the immediate aftermath of the bloodiest day of Burundi’s escalating crisis,” the group said.

This month, U.N. human rights chief Zeid Ra’ad al-Hussein also called for an urgent investigation into the alleged mass graves. He said the “increasing number of enforced disappearances, coupled with allegations of secret detention facilities and mass graves, is extremely alarming.”

Samantha Power, the U.S. ambassador to the United Nations, said Friday that the reports of mass graves “underscore the futility of trying to cover up such crimes.”

Burundi’s government has dismissed the allegations, saying they are based on false information supplied by the regime’s opponents.