GENEVA - The World Health Organization on Wednesday urged health workers around the world to report any patient with acute respiratory infection who may have travelled to Saudi Arabia or Qatar and been exposed to a new SARS-like virus confirmed in two people so far.

The United Nations agency put out a global alert on Sunday saying a new virus had infected a 49-year-old Qatari who had recently travelled to Saudi Arabia - where another man with an almost identical virus had died.

The Qatari remained critically ill in hospital in Britain, according to the WHO's latest information as of Tuesday.

The WHO said on Wednesday no new case of acute respiratory syndrome with renal failure due to the new virus had been reported but its investigations continued.

"We've got things in place should things change, should the behaviour of the virus change," spokesman Gregory Hartl said.

The WHO said it was working closely with Saudi authorities regarding health measures for the haj pilgrimage to Mecca next month when millions of Muslims travel to the kingdom and then return to their home countries.

Its clinical guidance to 194 members said health care workers should be alert to anyone with acute respiratory syndrome that may include fever?and cough, requiring hospitalisation, who had been in the area where the virus was found or in contact with a suspect or confirmed case within the previous 10 days.

The WHO said it was identifying a network of laboratories that could provide expertise on coronaviruses to countries.

"Though it is a very different virus from SARS, given the severity of the two confirmed cases so far, WHO is engaged in further characterizing the novel coronavirus," it said, referring to genetic sequencing.

Hartl, speaking to reporters on Tuesday, said: "This is not SARS, it will not become SARS, it is not SARS-like."

It was not established whether the virus spread by human to human contact or just how it was transmitted, he said.

"We don't know if all cases of infections are as severe as the two cases we have currently or in fact whether there have been 2 million cases of this virus and only 2 severe cases."