Wallström has joined leaders from more than 50 countries at the Nuclear Security Summit in Washington, which ends on Saturday.
Referring to the recent terror attack in Brussels and reports that IS sympathisers had spied on a nuclear energy expert there, Wallström said: "After what happened in Belgium, we can all see that this isn't something remote. It’s a threat that affects us today, a real threat that we need to tackle."
Although it is unlikely that terrorists could get a hold of enriched uranium or plutonium, many countries are still aware of the risk.
According to Wallström, Sweden has increased security in nuclear plants since 2007 and stepped up protection of radioactive materials such as caesium 137, which is used in cancer treatments but could also be placed in explosives and contaminate large areas.
The Nuclear Security Summit is the last of four meetings, with the first hosted by Barack Obama in 2010. But cooperation for an increased nuclear security will continue and Wallström has offered Sweden's help to convince more countries to ratify two legally binding conventions on nuclear terrorism and nuclear materials.
"We are ready to join a group of countries that commit to following up on the agreements reached here. We will continue to cooperate actively in the future," Wallström said.