Just days after they were killed in an ambush in the Democratic Republic of Congo on Thursday, the bodies of 15 Tanzanian peacekeepers have been repatriated. The soldiers were part of a United Nations peacekeeping operation in the conflict-torn eastern part of the country.

Read: Rebels attack UN peacekeepers in DRC, with more than a dozen dead and scores wounded

The assault, which UN secretary general Antonio Guterres labeled "the worst attack on UN peacekeepers in the organization's recent history", has been blamed on the Allied Democratic Forces (ADF) – one of the region's deadliest rebel groups.

Phil Clark, a political scientist at SOAS, the University of London, agrees that the ADF rebel group "looks the most likely suspect at this stage."

But he cautions that "until there is a more thorough investigation, we won't know for sure who was behind this."

Cause for speculation

Apart from the uncertainty surrounding the attackers, it is also unclear why peacekeepers at the UN base were unable to call in support from units elsewhere in the province during an attack that supposedly lasted 12 hours, Clark says.

If it was an ADF attack, however, "it shows a considerable escalation of the ADF's capabilities," the DR Congo expert told DW.

The rebels seem to have become more dangerous over the past months, he added – which begs the question of who has been supporting them, and how they got their hands on the necessary military equipment.

"It's caught many people off guard," Clark says.

The peacekeeping base is home to the UN mission's rapid intervention force and located about 45 kilometers from the town of Beni in North Kivu province in DR Congo's eastern region, which has been repeatedly targeted by ADF rebels.

Nearly 300 peacekeepers have been killed since the UN mission arrived in 1999, according to UN peacekeeping data

Period of political uncertainty

Clark sees the ADF capitalizing on a general situation of instability in Congo. The country's president, Joseph Kabila, was supposed to step down at the end of 2016 but the ballot to replace him has been continually delayed with elections now scheduled for December 2018.

The "scale of the (ADF's) ambition seems to be different" from other groups taking advantage of the fragile security situation, Clark said. "The ADF is now one of the most powerful groups in eastern Congo," the expert says, adding last week's assault might mean they are trying to push the peacekeeping force out of the region. 

The attack also puts a "spotlight on the weakness of the UN mission" that has been "largely ineffective in doing its task, which is protecting the local civilian population from attacks by a whole range of rebel groups," the political scientist says.

Escalating situation

The UN must renew its focus on the rebel groups, and the ADF in particular, the London-based political scientist says, pointing out that the force intervention brigade, which has been in place for more than two years, has failed to fulfill its mandate that specifically includes targeting the ADF.

Clark urges increasing resources and moving peacekeeping personnel from other parts of Congo to North Kivu, although he concedes that this will be difficult as the UN is already overstretched.

Jean-Pierre Lacroix, UN Under-Secretary General for Peacekeeping Operations, says the ADF has an "ideological and extremist" agenda, but is "also very much focused, as many other groups in that region, on the exploitation of illegal resources – and this is an area that is particularly rich in these different resources."

Challenging conditions

Meanwhile, DR Congo President Kabila, as well as the heads of state from neighboring Congo-Brazzaville and Angola, have called on the international community to classify the ADF as a terrorist group.

Analyst Clark is wary of this move, however.

The ADF may have been some kind of lslamist group in its early days around 2003, he says, "but if you look at the ideology of the group now, there is very little of this Islamist terrorist dimension."

"It's yet another rebel force, just more agile and powerful than many of the others."