Belgium is the EU country with the highest per capita number of fighters who have joined jihad in Syria and Iraq
Reynders told a press briefing in Brussels there is "concern" that "foreign fighters" were increasingly returning to Europe as US-backed coalition forces drive Islamic State group from territory in Syria and Iraq.
"Today, thanks to the progress that we are making with the military coalition in Iraq and in Syria, we see that cities and entire provinces are being recovered," Reynders said, flanked by French counterpart Jean-Marc Ayrault.
"But there is concern about the larger return of these foreign fighters to our countries," Reynders said following talks with Ayrault two days after the anniversary of the Paris jihadist attacks that were planned in Belgium.
He called for reinforcing not only "the cooperation and exchange of information between France and Belgium, but also with many other European partners and beyond."
The countries already stepped up cooperation after the attacks across Paris on November 13, 2015 that killed 130 people and put Belgium in the spotlight for alleged intelligence failures.
Belgium came under further fire after the same cell, investigators believe, that mounted the Paris attacks carried out suicide bombings at Brussels airport and a metro station on March 22 that killed 32 people.
The Paris and Brussels attacks were both claimed by the Islamic State group.
Reynders said that Brussels and Paris first increased intelligence cooperation after French national Mehdi Nemmouche allegedly shot and killed four people at the Jewish museum in Brussels in May 2014 following his return from war-torn Syria.
Nemmouche has been linked to Abdelhamid Abaaoud, who had fought in Syria, grew up in Brussels and died in a French police raid days after taking part in the Paris attacks.
Belgium is the EU country with the highest per capita number of fighters who have joined jihad in Syria and Iraq, a figure estimated at 465.
Both Reynders and Ayrault hailed progress in intelligence cooperation between both countries.
"Not only are we cooperating already, but the cooperation is tighter and much more fluid," Ayrault said.