A force of about 200 unidentified armed assailants ambushed a supply convoy in South Sudan on Tuesday, killing five U.N. peacekeepers and seven civilians, U.N. officials said.

The ambush marked the deadliest armed attack on the United Nations since the region became engulfed in intercommunal violence between warring ethnic groups. It also raised concerns that the United Nations has become a target in that violence.

All five peacekeepers were identified as Indian nationals.

“This was a direct targeted attack against the United Nations; this was not a case of us getting caught in the crossfire,” said Kieran Dwyer, a spokesman for the United Nations’ peacekeeping department. “It was a sustained attack with the intention to kill and sustain a firefight.”

The U.N. convoy, which included 18 civilians and a protection force of more than 30 peacekeepers, was traveling in Jonglei state when it came under fire, Dwyer said. The U.N. peacekeepers, he said, “fought back hard” and prevented the assailants from overwhelming the convoy and “killing everyone.”

The U.N. Security Council issued a statement condemning the attack, offering condolences to India and the families of the victims, and calling on the South Sudanese government to “swiftly investigate the incident and bring the perpetrators to justice.”

The attack is also expected to prompt a review of the U.N. force’s security procedures.

Hilde Johnson, a Norwegian national who serves as the U.N. special representative for South Sudan, expressed condolences to the families of the dead and vowed the United Nations’ support for peace efforts in the region. “This attack will not deter UNMISS [the U.N. Mission in the Republic of South Sudan] and its peacekeepers from working to protect vulnerable communities in South Sudan,” Johnson said.

For years, Jonglei state has been the scene of fighting between the Murle and Lou Nuer communities, who have engaged in deadly tit-for-tat cattle raids. The fighting peaked in December 2011, when thousands of young men from the Lou Nuer attacked the town of Pibor, burning homes and killing more than 1,000 people.

Trying to restore calm, South Sudan’s army has sought to disarm the groups. But the effort has been marred by reports of government human rights abuses, particularly targeting the Murle, who suspect that the government favors their rivals and have refused to turn over their weapons, according to Jehanne Henry, a researcher with Human Rights Watch.

“It’s clear that Jonglei is a problem that has not been solved,” Henry said.