Brussels - Belgian authorities spotted Paris attacks suspect Salah Abdeslam posing on Facebook with an Islamic State flag three weeks before the November 13 massacre, but failed to follow up, Belgian broadcaster RTBF reported Tuesday.
Although the national terror threat centre was told about the photo in October, security officials failed to take a closer look, RTBF said, without identifying its sources.
The revelation is the latest example of failures by Belgian police in the months leading up to the attacks in the French capital that killed 130 people.
RTBF also said Abdeslam was known to have been in contact in early 2015 with suspected attacks ringleader Abdelhamid Abaaoud, who was already known as an important figure from the Islamic State group.
Both men, as well as several others involved in the attacks, are from the gritty district of Molenbeek in Brussels.
Last month, a parliamentary panel heard that Belgian police abandoned a probe into Abdeslam and his brother Brahim six months before the Paris attacks, despite flagging them as priority terror suspects.
This allegedly allowed Abdeslam to go ahead with preparing the attacks. His brother Brahim would eventually blow himself up in a Paris cafe on the night of the massacre.
Salah Abdeslam, the sole surviving suspect in the November 13 terror attacks, was arrested in Brussels on March 18 after four months on the run as Europe's most wanted man.
He is now in France awaiting trial over his alleged role in the killings.
Abdeslam has also been linked to several jihadists directly involved or implicated in the bomb attacks in Brussels on March 22, just four days after his arrest.