Thai authorities took nearly four days to confirm the country's first case of Middle East respiratory syndrome, the Health Ministry said on Friday, a time lag likely to raise fears of a further spread of the deadly virus in Asia.

Thailand had confirmed its first case of MERS on Thursday, a 75-year-old businessman from Oman, just as an outbreak in South Korea appeared to be leveling off. The South Korean outbreak, which began last month, has infected 166 people and killed 24 of them.

In Thailand, the infected man arrived in Bangkok on Monday on an Oman Air flight for medical treatment for a heart ailment at a private hospital.

Public Health Minister Rajata Rajatanavin declined to identify the hospital and said the patient had been put in quarantine at an infectious diseases institute in Bangkok on Thursday.

"It took about four days to diagnose this case and two lab tests," Rajata said.

Authorities wanted to monitor all 106 people on board the man's flight, Rajata said, though it was not clear how everyone could be traced.

Among those being monitored were the man's two sons, who were considered at high risk because of their proximity to their father. The two had been tested and results were due later on Friday, Rajata said.

Most of those under observation had been told to stay at home for 14 days.

The Thai case will compound fears in Asia of a repeat of a 2002-03 outbreak of SARS, which killed about 800 people globally.

MERS was first identified in humans in Saudi Arabia in 2012, and the majority of cases have been in the Middle East.

Isolated cases have cropped up in Asia before South Korea's outbreak began last month, and Thailand is the fourth Asian country to register a case.

China has had one case recently, that of a South Korean man who traveled to China via Hong Kong despite authorities suggesting he stay in voluntary quarantine at home.

South Korea's outbreak, the largest outside Saudi Arabia, has been traced to a 68-year-old man who returned from a business trip to the Middle East in early May.

South Korean health officials said on Friday that the MERS outbreak appears to have begun subsiding, as it reported one new case - the lowest rate of new infections in two weeks.

This brought to 166 the total number of confirmed cases of the disease in the country since the first was confirmed on May 20, the Health Ministry said.

The number of people in quarantine had fallen 12 percent from Thursday to 5,930.

The government of South Korean President Park Geun-hye has come under attack for its perceived inadequate initial response. Park's approval rating has declined to its lowest level since she took office in February 2013, a survey showed Friday.

Park's support rate was 29 percent this week, according to the survey of 1,000 adults by a pollster Gallup Korea. That figure was down 4 percentage points from the prior week.

Also on Friday, a South Korean village that was put under quarantine was opened up after two weeks of isolation, allowing its population of 102 people to resume normal activities.

Reuters - AFP - Xinhua