JERUSALEM -- Israel's military said on Tuesday that it had started "a precise counterterrorism operation" in Rafah city in the south of the Gaza Strip and assumed "operational control" over the Rafah crossing in Gaza.

The crossing, which has served as a passage for humanitarian aid from Egypt to war-torn Gaza, was out of service.

Since the beginning of the assault overnight Monday, Israel said it has taken control of the Gaza side of the Rafah crossing, with the Israeli forces killing at least 20 militants.

Israeli forces attacked the Rafah city from the ground and air, the military said, as residents reported heavy and relentless bombardments.

The military said it had struck "military structures, underground infrastructure, and three operational tunnel shafts."