Taiwan on Tuesday raised its alert level on travel to South Korea.

The move follows North Korea's artillery attack on a South Korean island last week and the ongoing joint military exercise between South Korea and the U.S.

Taiwan's Foreign Ministry raised the alert to "red" for travel to the five South Korean islands near the maritime border with North Korea, saying that visits to the islands should be avoided.

The alert level for travel to the rest of South Korea was raised to "yellow," which means that Taiwanese people should only travel there if the trip is absolutely necessary.

Taiwan’s travel alert for South Korea had been at the lowest level of “gray” up until the North's artillery attack. Taiwan’s travel alert for North Korea is currently at “orange.”

Taiwan's travel alert has four levels: gray, yellow, orange and red in ascending order of danger.