China said it downed a Vietnamese jet fighter in one of the most serious incidents along the tense Sino-Vietnamese border since the two former allies fought a 17-day war along their common boundary in 1979 after Vietnam's invasion of Cambodia. The official New China News Agency said China's air force shot down a Vietnamese MIG-21 after it intruded as far as 20 miles into southern China. The report said China's Foreign Ministry had "made representations" to Vietnam's ambassador about the violation of Chinese airspace. "The Vietnamese authorities must adopt practical measures to put an end to such incidents or they will be responsible for all the consequences," the news agency said. Since 1979, there has been sporadic fighting along the border, with each side claiming attacks by the other.