About a dozen additional countries and parts of China have slapped entry restrictions on travelers from South Korea, and the United States has raised its travel warning for its Asian ally as the wave of new coronavirus cases in the country showed no signs of let-up.

The State Department's travel advisory was raised by one notch to Level 3, the second-highest on a four-tier scale. Level 4 advises people not to travel to the designated country. The US has not put any entry restrictions from travelers from South Korea, however.

US President Donald Trump said it is not the right time to restrict travel to and from the country.

Five provinces in China have tightened quarantine processes for international air travelers, with some restrictions applying to all passengers and some only to those coming from South Korea or Japan, according to Seoul's foreign ministry website Thursday.

Mongolia, Fiji, the Philippines and the Seychelles imposed entry bans on South Korean nationals and visitors who have been in the Asian country for the past two weeks. Seven others, including India, French Polynesia, Belarus, Morocco and Paraguay, toughened their quarantine procedures.

That raises the total number of foreign countries that have enforced such restrictions for South Korea to 42 on Thursday, up from the previous day's 30. 

South Korea has seen a rapid rise in the number of coronavirus cases in recent weeks. On Thursday morning, the Korea Centers for Disease Control and Prevention reported an additional 334 new cases, bringing the total to 1,595 cases and 13 deaths.

South Korea has stepped up diplomatic efforts to persuade other countries to refrain from entry bans. Foreign Minister Kang Kyung-hwa spoke by phone with Chinese Foreign Minister Wang Yi on

Wednesday and expressed concerns about restrictions imposed by provincial Chinese governments.

"We know that our people are very much worried. We've protested strongly to some governments that took the measures without prior notice, and our diplomatic missions are actively negotiating with other countries so as to not cause any situation that may baffle

our citizens," Kang told reporters at Incheon International Airport upon returning from a trip to Europe.

"Even though the confirmed infection cases are on the rise, the assessment by the international community and the (World Health Organization) is that they trust our capabilities," she added.

The Chinese measures have raised the ire of South Koreans as they came despite Seoul's rejection of public calls for an across-the-board entry ban on Chinese tourists in line with

Beijing's demand for "scientific" decisions on travel restrictions.

Chinese Ambassador to Seoul Xing Haiming said Wednesday the quarantine measures by the provincial authorities are not intended only for South Koreans and that the two sides are working closely together to bring the virus under control.

The foreign ministry has also come under fire for holding back on including China in a list of countries toughening entry restrictions against South Koreans, with critics accusing the ministry of being too mindful of China.  Ministry officials said it took time to verify the restrictions. (Yonhap)