South Korea's health ministry, which reported four new cases of Middle East Respiratory Syndrome (MERS) on Wednesday, said the outbreak was at a crossroads, backing off from its earlier view that the spread of the often-deadly virus had leveled off.

The more guarded assessment came as the government extended the partial shutdown of Samsung Medical Center in Seoul, which had been due to end on Wednesday. About half the 179 infections in the country have been traced to the prestigious hospital, including some of this week's new cases.

"We are at a crossroads, whether this is going to spread further or not," Kwon Deok-cheol, the health ministry's chief policy official, told a news briefing.

"As of now we can't answer that part because additional cases have occurred, although we thought until last weekend it had leveled off," he said when asked if there was any change in its earlier view that the outbreak had settled.

The country reported no new MERS case on June 20 but since then 13 fresh cases have been confirmed. During the peak of the outbreak early this month, new infections exceeded 20 on some days.

A total of 67 people who had tested positive for the MERS virus have recovered and been discharged from hospital since the outbreak started in May, while 27 patients have died.

South Korea's outbreak of the virus is the largest outside Saudi Arabia.

On Tuesday, the heir apparent of South Korean conglomerate Samsung Group [SAGR.UL] bowed in apology during a nationally televised address for the failure to stop the spread of the virus at the hospital run by a group foundation.