Belgian officials on Monday raised the death toll from last week's devastating "Islamic State" (ISIS) suicide attacks on Brussels airport and the metro to 35, AFP reports.

Officials from the government's crisis centre said 31 people died at the two attack sites and four had died in hospital. Three bombers were also killed.

Health Minister Maggie De Block tweeted: "Four patients deceased in hospital. Medical teams did all possible. Total victims: 35. Courage to all the families."