It's become the United Nations' worst-case scenario for Iraq: greater gains by the self-proclaimed "Islamic State," known as ISIS or IS. Given the international offensive against the militants is faltering, the UN is bracing itself for more IS attacks on "a growing number of cities," says Dominik Bartsch, Deputy Humanitarian Coordinator for Iraq.

Bartsch presents a colorful map of Iraq during this interview in Berlin. Several cities, including Falluja and Tikrit, are highlighted with angry red circles. It's likely, he says, that there "would soon be many Ramadis" - referring to the capital of Anbar province, which fell to the extremists last month.

DW: How many cities are in danger of falling to IS at this point?

Bartsch: We're currently assuming that a number of the urban agglomerations along the northern axis from Bagdad all the way up to Mosul may witness some fighting in the months to come. Whereas previously we were focusing on the contingency planning for a possible outflow of displaced people from Mosul, we are currently far more concerned that those smaller cities - and there is quite a number of them - may also generate new waves of displacement.

What kind of numbers are we talking about?

In the worst case scenario, up to one million Iraqis may be displaced in the context of the counter-offensive, leading all the way up to Mosul. Mosul itself currently has a civilian population of more than 1.5 million inhabitants, so that of course would be another scenario, should the confrontation reach Mosul itself. We hope that that is not the case, but recent developments have shown that it will take longer than previously anticipated to dislodge IS and to really ensure that the population in those areas has access to proper assistance.

Is the Iraqi government at all prepared to deal with this kind of influx of internally displaced people?

I believe that the Iraqi government, together with the Kurdish autonomous region of Kurdistan, is really trying its level best to provide support to those displaced, the vast majority of whom are Iraqis. The challenge is that right now that the Iraqi government is out of cash. So the ability to respond, to run social welfare programs, to provide for basic infrastructure, to scale up health facilities, to support the additional population in the schools - all of that is falling into disrepair, simply because the funding is not there. One principal factor of the Iraqi government running out of money is a drop in the price of oil, which has resulted in a situation which makes it very difficult for the Iraqi government to sustain its commitments. Unfortunately, this comes at a current funding crunch in the international community. The net result is that our standards of assistance have dropped quite drastically and that has created a situation where we are really prioritizing life-supporting interventions.

In the past we've seen regional actors stepping in to provide humanitarian assistance, such as Saudi Arabia and even Iran. Which role are those actors likely to play now?

We are very hopeful that some of the governments in the region will support the humanitarian effort, be it as donors, be it as supporters to the humanitarian requirements, or exerting political influence leading to the resolution of the conflict.

There have been reports of refugees being reluctant to return to Sunni areas liberated by Shiite militias. Can you confirm that there is indeed a sectarian dimension to the refugee crisis?

There are underlying dynamics: Obviously there is a very worrisome upsurge in sectarian tension between Sunnis and Shias. This also manifests itself in a perception that if Shiite militia were part of the liberation, this would have a bearing on how the Sunni population would perceive that liberation. We are primarily concerned with those who are affected by this conflict and to this extent it really is immaterial what their religious affiliation is: they're first and foremost victims and they need our support.

Do you provide assistance to areas controlled by IS?

There are efforts under way to try and understand the dynamics at the level of the community and where possible to try to see if support can be extended to these, what we call, hard-to-access areas. It would not, however, include formal negotiations for access.

So you would work with local humanitarian NGOs?

Yes, that's correct.

Dominik Bartsch is Deputy Humanitarian Coordinator for the UN in Iraq. The UN has launched an emergency appeal to the international community, asking for $500 Million (445 million euros) to cover its humanitarian operations in Iraq until the end of the year.