Four of the five North Korean sailors rescued last week by South Korea's Coast Guard in the East Sea have returned home while one decided to defect, a government source said Sunday.

The South Korean authorities repatriated the four on Friday, four days after the Coast Guard rescued their ship, which was spotted floating adrift due to an engine problem in waters off the eastern coastal city of Sokcho on Monday.

"Of the five rescued North Koreans, we returned four based on their free will," the source said.

Some observers said that the North could respond angrily to the one sailor's decision to remain in the South. 

In 2015, the South repatriated only two of the five crewmembers of a rescued North Korean vessel. At the time, Pyongyang issued a Red Cross statement, claiming that the South was forcibly holding the remaining two.

But last June when a similar case occurred, the North did not issue any angry response.

It is not uncommon for North Korean fishing boats to end up in South Korean waters due to engine or other mechanical problems. The South has consistently repatriated crew members if they want to go back.(Yonhap)