North Korean border troops fired on a group of Chinese citizens last week possibly because they were suspected of being South Korean spies, a Chinese newspaper said on Wednesday, citing officials from the North.

The border guards shot at the Chinese nationals crossing the river border near the northeastern Chinese city of Dandong on Friday, killing three and wounding a fourth, China's Foreign Ministry said on Tuesday, prompting a rare complaint from China, the North's only major ally.

The report in the Global Times newspaper said North Korea had raised its vigilance in the wake of tensions with South Korea over the sinking of a South Korean navy ship, the Cheonan, in March.

China's 1,415-km (880-mile) border with its neighbour is guarded by troops on both sides, but the river dividing them is often narrow and vulnerable to smugglers and refugees passing from the North into much richer China.

Chinese Foreign Ministry spokesman Qin Gang said the people were suspected of smuggling. But the Global Times, a popular tabloid, said North Korea's explanation was that its troops may have believed the border crossers were spies.

"The North Korean side explained that because of the Cheonan incident, they have raised their vigilance," the paper said, citing Chinese border authorities. The paper did not name its sources.

"The Chinese border residents spoke Korean and were wearing camouflage clothing, and the North Korean soldiers may have believed they were South Korean spies and so opened fire."

Many Chinese residents near the border with North Korea are ethnic Koreans.

The North Korean authorities said they were willing to compensate the families of those killed and "hoped that this incident will not hurt Chinese-North Korean relations", the Global Times said.

The North's leader, Kim Jong-il, visited China early in May, on a rare trip abroad.

Reuters