Two Chinese fishermen were facing formal arrest by South Korea after they were believed to have injured four South Korean fishing officials who boarded their vessel, South Korean media said on Tuesday.

The vessel had been suspected of illegal fishing.

The two - the 36-year-old captain and a 29-year-old navigator - are among nine Chinese fishermen who were detained early on Monday after the conflict with the South Korean officials on the Yellow Sea, Yonhap said.

The South Korean coast guard imposed 15 million won ($13,292) bail for the release of the detained fishing boat. The remaining seven Chinese sailors were freed because they were not involved in the attack, said Yonhap.

All nine Chinese fishermen are now at the Mokpo port in South Korea, according to China Central Television.

Yonhap earlier reported that the four injured officials work for South Korea's West Sea Fisheries Supervision Office, which is affiliated with the Ministry for Food, Agriculture, Forestry and Fisheries.

The ministry on Tuesday filed a protest over the attack to He Ying, consul general of the Chinese embassy in South Korea.

China felt "sad" about the conflict and promised to further promote the education of its fishermen to prevent similar attacks in the future, the Chinese official was cited by Yonhap as saying.

Beijing is working together with Seoul to verify the details of the conflict, the Chinese Foreign Ministry said on Monday.

China hopes South Korea can guarantee the safety and legitimate rights of the fishermen, and will keep contact with South Korea to solve the issue appropriately, the ministry said. South Korea has vowed a tougher reaction to illegal fishing by Chinese boats since a Chinese captain killed a South Korean coast guard officer in a conflict last December.

In mid-April, the local court of Incheon City, in South Korea, gave Cheng Dawei, the captain, a sentence of 30 years in jail, with a fine of 20 million won.

However, China does not accept South Korea's unilateral application of the Exclusive Economic Zone law on the verdict, according to Chinese Foreign Ministry spokesman Liu Weimin, as the two countries have not yet delineated the border of the EEZ in the Yellow Sea.

Cheng and nine other fishermen were fishing in the Yellow Sea on Dec 12 when the South Korean coast guard officer led two other policemen to arrest Chinese fishing boats in that area.

During the confrontation, the captain accidentally stabbed the official to death, and injured another in the stomach. In the end, the captain and nine other crew members were detained and escorted to Incheon.

During his visit to China in January, South Korean President Lee Myung-bak discussed the issue of illegal fishing with Chinese President Hu Jintao, and the two sides have pledged to continue regular meetings to resolve the issue.

Contact the writer at zhouwa@chinadaily.com.cn