Iraqi authorities believe more than 130 civilians were killed in strikes over several days in Mosul's al-Jadida area, and attention has focused on one particularly deadly attack on March 17. Other estimates say as many as 400 people may have died.
"We have opened a preliminary investigation to establish ... whether all procedures were observed during two incidents," prosecutors' spokesman Eric Van Der Sypt told AFP news agency.
"If rules of engagement were properly observed ... it is possible that no crime was committed," Van Der Sypt said.
Belgian MP Wouter De Vriendt told Flemish broadcaster VRT the case involved strikes carried out by Belgian F-16 fighter jets on March 17.
The US-led coalition had previously said it carried out a strike on March 17 in an area of west Mosul in which civilian casualties were reported, and it had opened an investigation.
The coalition insists ISIL has targeted civilians and used them as human shields, while acknowledging air strikes by anti-ISIL forces have also left civilians dead.
General Stephen Townsend, the senior US commander in Iraq, said this week a coalition strike in the northern city earlier this month "probably" killed dozens of civilians.
US investigators are also looking at the apparent bombing of a school in Mansura near Raqqa, Syria on March 21, and a building next to a mosque on March 16 in al-Jineh, in Aleppo province.
Source: AFP news agency