Fear of swine flu is expected to reduce the number of pilgrims attending this year's Hajj pilgrimage, a senior Saudi official says, BBC reported.
Gen Mansour al-Turki told the BBC that although the number of international visitors might not be affected, a 40% drop in domestic pilgrims was expected.
The BBC's Shahzeb Jillani says it is the first official recognition that fear of swine flu may affect the Hajj.
About two million Muslims converge on Mecca each year for the pilgrimage.
Estimating the number of Hajj pilgrims has never been easy, our correspondent in Mina says, and officials hope to have a clearer picture by the end of the week.
Saudi health authorities announced at the weekend that four people attending the Hajj had died from the H1N1 virus, but played down the risk to other pilgrims.
"There is no risk of the illness spreading as we are well-prepared and have taken the necessary measures," health ministry spokesman Dr Khaled Marghlani told a news conference on Tuesday.
'More cases detected'
The ministry said the four who died were a Sudanese man, a Moroccan woman and an Indian man - all aged over 75 - and a girl aged 17 from Nigeria.
The statement said the four had not followed "recommended procedures, especially vaccination against swine flu".
The ministry said 16 other cases had been detected and four were in a critical condition.
Pilgrims are due to start the Hajj rites on Wednesday.
They begin with the "tawaf", walking seven times round the Kaaba - the cube-like building in the centre of the Grand Mosque - in an anti-clockwise direction.
Pilgrims then go to Mina to spend the night before climbing Mount Arafat on Thursday.
The hajj has been the scene of several tragic accidents caused by huge crowds.
In 2006, 364 people were killed in a stampede at the entrance to the Jamarat bridge in Mina.
In a bid to avoid a repeat of the disasters, authorities have just completed the rebuilding of the bridge.
Officials say the 950m (3,135ft) long, 80m (260ft) wide five-storey pedestrian walkway, which cost $1.2bn (£723m), will prevent overcrowding.