A historically important city in world wars, Paris will host yet another international conference Monday to divide responsibility in confronting the Islamic State.

About 20 countries are slated to participate, but Iran has refused, despite recently stating their interest in fighting the militants.

"This conference will allow everyone to be much more precise about what they can do or are willing to do," a French diplomatic source told Agence France-Presse (AFP).

But, in order to protect the military strategy from being known to the common enemy, few details will be made public.

"We're not going to say who is going to carry out air strikes. Or when they might happen," the source told AFP.

The conference will be co-hosted by French President Francois Hollande and Iraqi President Fuad Masum, will be mostly attended by foreign ministers, including U.S. Secretary of State John Kerry.

Kerry has been in the region for the past several months garnering support against IS, formerly ISIS and ISIL.

But one important neighbor, Iran, is not participating in the conference.

Iran's Foreign Ministry Spokeswoman Marzieh Afkham has questioned the sincerity of the coalition of countries, Press TV reported.

Deputy Foreign Minister for Arab and African Affairs Hossein Amir-Abdollahian echoed the doubts, saying that it is a selective group of countries that were invited and is just for show.

He said that the country would rather support a universal front against terrorism, rather than a elective coalition against a specific group.

"The Islamic Republic of Iran is the first country that rushed to help Iraq in the fight against terrorism. We will continue our strong support for Iraq and Syria in the fight against terrorism," Amir-Abdollahian said.

Iran has had ties to the Assad regime in Syria, a point of contention with many of the Western allied powers who have discredited Assad's government, AFP reported.

Both Iran and Turkey are tricky countries to deal with because of their proximity to the conflict and the presence of IS within their borders.

Turkey shares borders with Syria and Iraq and remains a close U.S. ally with the NATO alliance, but since IS militants are holding 49 Turkish citizens, including children and diplomats, they also require a different approach to the situation.

Currently IS has control over 40 percent of Iraq and about a quarter of Syria, and though Bashar al-Assad has expressed interest in a coalition, some countries are hesitant, while others, like France, have outright rejected the idea.

The focus of the conference Monday will be Iraq since that is where the majority of the Islamic State militants currently have control.