A spokesman for Belgian Justice Minister Koen Geens confirmed that several people were arrested in Molenbeek district during searches in connection with Friday's terror attacks in Paris, Xinhua reported citing Belgian TV channel RTL.
Two cars used by the terrorists in the attack bear Belgian number plates, said RTL.
At least 127 people were killed as eight terrorists armed with automatics and in suicide vests unleashed Mumbai-style mayhem in six crowded parts of Paris on Friday night.
The holder of a Syrian passport, which was found near the body of one of the gunmen who died in Friday night's attacks in Paris, passed through Greece in October, said a Greek minister, and another suspected attacker was thought to have entered Europe the same way.
"The holder of the passport passed through the island of Leros on 3 October, 2015, where he was identified according to EU rules," said Greece's deputy minister in charge of police Nikos Toskas in a statement.
Toskas did not know if the Syrian passport had been checked by other countries through which the holder might have passed on his way to France.
A Greek Police source said the passport's owner was a young man who had arrived in Leros on a small vessel from Turkey with a group of 69 refugees and had his fingerprints taken by Greek officials.
Three Greek government sources later said a second suspect was also very likely to have come into Europe through Greece, adding that an investigation was still under way.
Any identity documents and fingerprint records would have to be matched with the remains of the actual attackers to establish whether they passed through Greece posing as refugees, or perhaps bought or stole passports along the way.
Following the Paris bloodshed, populist leaders around Europe rushed to demand an end to an influx of refugees and migrants from the Middle East and Africa. Poland said it could not accept migrants under EU quotas without security guarantees.
If one or more of the attackers turn out to have come into Europe among the migrants arriving from war-torn countries, this could change the political and security debate about refugees and what to do with them.
The police declined to give the name of the Syrian passport holder, saying French authorities wanted to keep information about the suspect confidential.
The source said there were no official records showing the man had left Greece, but that authorities believed he may have crossed into Macedonia.
The Greek Police were also asked by French authorities to check on the holder of an Egyptian passport that was apparently found near the body of another attacker, said the police source.
Greece has seen about 600,000 refugees and migrants â€” mainly from Syria, Afghanistan and Iraq â€” arrive on its shores this year, mostly from nearby Turkey, hoping to reach wealthier northern Europe.
The island of Leros, in the southern Aegean sea, is one of five preferred entry points where Greek authorities have been setting up so-called hotspots to register and identify arrivals.