WASHINGTON–European governments must integrate Muslims more into their community to curb the rise of homegrown terrorists like those responsible for the recent Paris attacks in which 20 people died, experts said Tuesday at a talk hosted by the International Institute for Strategic Studies.

Four men have been charged with association with terrorism for their roles in the hostage-taking at a kosher supermarket and the earlier attack at the weekly newspaper Charlie Hebdo. At least one of those involved is associated with the Islamic State.

The event Tuesday featured Angel Rabasa, a senior political scientist at the RAND Corporation, a nonprofit research organization; and Jackson Janes, president of the American Institute for Contemporary German Studies at Johns Hopkins University. Around 30 people attended the event.

An estimated 5,000 European citizens have joined the armed conflict in Syria and pose a direct threat to their home countries upon return, Europol announced this month.