The World Health Organisation (WHO) after a five-day mission to Jeddah pinpointed breaches in its "recommended infection prevention and control measures" as being partly responsible for an increase in infections in the Red Sea city.
The disease, which first appeared in the kingdom in September 2012, has now infected a total number 449 Saudis, accounting for the bulk of cases registered across the globe.
Two of the latest deaths reported late on Wednesday -- of a 65-year-old woman suffering from several illnesses and a 45-year-old woman -- occurred in the capital Riyadh. Both died on Tuesday.
In Jeddah, the commercial capital, a 70-year-old woman died on Monday and a 60-year-old man died on Tuesday, the health authorities said.
Among the 18 people newly infected is a 10-year-old boy who was taken to a government hospital in Jeddah following an accident on April 29.
After he was discharged from the hospital on May 2, MERS symptoms began to appear and he was rushed to intensive care.
Saudi Arabia's acting health minister Adel Fakieh announced Tuesday the sacking of the head of Jeddah's King Fahd Hospital where a spike in MERS infections among medical staff sparked panic among the public.
The WHO said the recent increase in numbers of infections does not suggest a "significant change in the transmissibility of the virus".
"The majority of human-to-human infections occurred in health care facilities," it said, adding that "one quarter of all cases have been health care workers".
The team urged health care workers to improve their "knowledge and attitudes" about the disease.
MERS is considered a deadlier but less-transmissible cousin of the SARS virus that erupted in Asia in 2003 and infected 8,273 people, nine percent of whom died.
There are no vaccines or antiviral treatments for MERS, a disease with a mortality rate of more than 40 percent that experts are still struggling to understand.
Some researchers think it may originate in camels.
Fakieh on Wednesday announced an awareness campaign to help stop the disease's spread, urging people not only to follow strict measures of hygiene, but specifically to avoid sick camels and refrain from eating raw camel meat or drinking unboiled camel milk.