Syria has been so contaminated with weapons and bombs that the lives of 5.1 million people, including 2 million children, are at constant risk, an international aid group warned in a report released on Tuesday.

Handicap International, which helps the disabled during conflicts, called on all parties in the conflict to abide by international humanitarian law and immediately end the use of explosives in highly populated areas.

It also urged humanitarian groups to include lessons in their programs on how to spot, avoid and report dangerous ordnance.

Syria's conflict, now in its fifth year, has killed more than 220,000 people.

Hours after the report was released, two motorcycles rigged with explosives blew up in the central city of Homs, killing at least four people and wounding 28, Syria's state media said.

The Britain-based Syrian Observatory for Human Rights said the blasts occurred in neighborhoods that are mostly inhabited by members of President Bashar Assad's minority Alawite sect.

The Islamic State group, which has presence in the eastern parts of the province of Homs, claimed responsibility for the attacks which it said were targeting regime supporters. The group, in a statement posted on Twitter accounts and a website that carries militant statements, said two of its members were the suicide bombers.

The report by Handicap International said that between December 2012 and March 2015, the group analyzed 77,645 incidents -- such as fighting and bombardments -- and found that explosive weapons are the most commonly used weapons in Syria.

It said civilians "are in grave danger, as 75 percent of these incidents took place in populated areas." Handicap International said weapons have been used by all parties to the conflict and that the explosive weapons used include mortars, rockets, artillery shells, aircraft bombs, cluster munitions and mines.

It added that the capital Damascus and its suburbs suffered an average of seven incidents a day over the two-year period with a total of 5,353 incidents.

"With more than one million war-wounded in Syria, this is an entire generation who will suffer the consequences of those weapons," it said.