Just a few days before Haj, swine flu has reared its ugly head again, killing four pilgrims in Saudi Arabia.

An Indian man, a Moroccan woman and a Sudanese man -- all aged 75 -- died from the H1N1 virus, as had a 17-year-old girl from Nigeria - none of them had taken the vaccine.

An estimated 2.5 million Muslims are expected to converge in Saudi Arabia for this year's Haj, making it the world's largest gathering since swine flu began spreading around the globe after it was first reported in April.