"Yes, we are of course looking at building a relationship" with IS, ICRC Director-General Yves Daccord told AFP in an interview.
"We have a very clear humanitarian vision. First, what we see is 10 million people. Ten million people under the control of the Islamic State group (in Iraq and Syria).
"We are interested in these 10 million people. What happens to them? What are their problems? This is what will guide us," he said.
The emergence of armed groups which at times disregard the need for life-saving aid is one of the threats facing the ICRC and groups like it, Daccord said.
Organisations seeking to help civilians engulfed by conflict will increasingly need to connect with such groups, regardless of their ideology, he told AFP.
"My sense is, most of the international organisations will have to possibly rethink about how they operate in these areas, otherwise they won't be in a position to (work)," he said.
"You cannot just come from Geneva" and expect armed groups to let you operate.
"You don't build acceptance from Boko Haram or any armed group in Syria in one day. It takes a lot of time and you have to have the right people."
Daccord said it took several years of outreach to Boko Haram before the ICRC was able to work in the extremist group's northeast Nigeria strongholds.
Though perhaps less high-profile than IS, Boko Haram's atrocities are unrivalled, including the repeated use of children as suicide bombers and multiple massacres and abductions targeting students.
To operate in Boko Haram or IS areas, an organisation must be seen as totally "non-partisan," he said.
