At least one Rwandan was killed when shells landed in a village, as fighting between M23 rebels and the Congolese army backed by UN peacekeepers threatened to spill over into Rwanda. Rwandan Foreign Minister Louise Mushikiwabo issued a statement on her Twitter account saying "we have the capacity to determine who fired on us and we will not hesitate to defend our territory.”

DW: What shape or form could that defense of Rwandan territory take?

Phil Clark: That could take quite an extreme form of intervention by Rwanda. We have seen some reports of Rwandan troops grouping on the border with Congo. The Rwandan Foreign Minister has been on Twitter saying Rwanda hasn't yet invaded Congolese territory, but this is an option that Rwanda is certainly not ruling out. In the coming days we could see a serious escalation of the situation which could include Rwanda going into Congo.

A Rwandan official at the UN says the shelling was carried out by Congolese troops, UN peacekeepers say they have witnessed M23 rebels shelling Rwanda. Which version of events in the more probable?

As is often the case in violent conflicts, the truth is extremely murky. There is an enormous amount of propaganda in this situation. My own personal view is that it would be very unlikely for the M23 rebels to be firing into Rwanda, given the links between M23 and Rwanda in the past. It would make very little strategic sense. A more likely situation is that it's either the Congolese army or perhaps elements of the UN intervention force. The likeliest scenario is that it is the Congolese army that's firing into Rwandan territory. That represents a very serious moment. We haven't witnessed this kind of behavior in the last 25 years of this conflict.

You mentioned members of the international brigade, what possible motives could they have for firing into Rwandan territory?

We have seen in the last few days this new intervention brigade taking a very belligerent stand. Not just against M23 but at least in terms of the rhetoric a very belligerent stand towards Rwanda, given that Rwanda is suspected to be supporting the M23 rebels. The intervention brigade has made it clear that they don't just see the M23 as the problem but they also see Rwanda as part of the problem. It would be surprising if, in fact it was the UN brigade that was firing into Rwandan territory. But certainly we have seen the kind of language from the UN in the last few days that couldn't entirely rule out that possibility.

What do you make of the decision by the M23 to withdraw from the front lines and allow an investigation into the shelling of nearby towns, as well as give negotiations a chance?

The possibility of negotiations has been on the table for the last few months. In some ways, I believe this is what the UN intervention brigade is jeopardizing. The problem with the intervention brigade is that it has sent a message to the M23 that peace negotiations are no longer viable, that the regional conflict can now only be solved through the barrel of a gun.

Last year's report by a group of experts from the UN said Rwanda's Defense Minister was commanding the M23 rebels in Congo. It also accused Rwanda of arming the rebels. Is there any reason to doubt the veracity of that report?

What that UN report and the UN intervention brigade have done is to escalate the conflict. They have raised the stakes and exacerbated all the actors on the ground. The problem that the UN has generated through their report and the intervention brigade is effectively to have shut down negotiations, particularly between the Congolese and Rwandan governments.

Dr. Phil Clark is a lecturer in international politics at the School of Oriental and African Studies (SOAS) in London.