The U.N. health body put out a global alert on Sunday about the 49-year-old man who had recently travelled to Saudi Arabia - where it said a second patient with an almost identical virus had already died.

A senior British health official said there was no immediate cause for concern although experts were watching out for any signs of the virus spreading.

Any suggestions of a link between the virus and Saudi Arabia will cause particular concern in the build-up to next month's Muslim haj pilgrimage, when millions of people arrive in the kingdom from across the world, then return to their homes.

The virus, known as a coronavirus, comes from the same family as the SARS infection that emerged in 2002 and killed 800 people.

"This is now an international issue because we have a case in the UK and one in Saudi," WHO spokesman Gregory Hartl said.

"The (Qatari) patient is still alive but, as we understand, in critical condition," he said.

The Qatari man first showed symptoms of an acute respiratory infection and kidney failure while he was in Qatar, the WHO said.

He spent some time in intensive case in Qatar and was later flown to the UK where he was being treated in a London hospital, said authorities, declining to say which one.

Laboratory tests on the Qatari man showed his virus was almost identical to one that killed a Saudi patient earlier this year, the WHO said. The Saudi man's virus was not identified as a new kind of infection at the time of his death.

HEALTH AUTHORITIES ON ALERT

The WHO said it was in touch with health authorities in Britain, Qatar, Saudi Arabia and at the Stockholm-based European Centre for Disease Prevention and Control (ECDC.L)

"We're asking for information from whoever might have seen such cases, but as of the moment we haven't had any more notifications of cases," said Hartl.

Coronaviruses are a large family of viruses that includes causes of the common cold but can also include more severe illness such as the virus responsible for SARS.

SARS, or Severe Acute Respiratory Syndrome, appeared in China in 2002 and infected more than 8,000 people worldwide, killing around 800 of them before being brought under control.

Britain's Health Protection Agency HPA.L said it had conducted lab testing on Qatari case and found a 99.5 percent match to a virus that killed a 60-year-old Saudi national earlier this year.

"This new virus ... is different from any that have previously been identified in humans," the HPA said.

John Watson, head of the HPA's respiratory diseases department, added there was no evidence of ongoing transmission.

"In the light of the severity of the illness that has been identified in the two confirmed cases, immediate steps have been taken to ensure that people who have been in contact with the UK case have not been infected, and there is no evidence to suggest they have," added Watson

Peter Openshaw, director of the Centre for Respiratory Infection at Imperial College London said virus was unlikely to prove a major concern and experts hoped the two cases would turn out to be "just a highly unusual presentation of a generally mild infection".

The HPA is not recommending any specific action for members of the public or tourists and travellers, but said it would issue further advice as more information became available. (Additional reporting by Angus McDowall in Riyadh, editing by Andrew Heavens)

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