"If Chinese citizens are involved, we will... safeguard Chinese citizens' legitimate rights and interests in accordance with the law," foreign ministry spokeswoman Mao Ning said.

Relations between Kyiv and Beijing, a key Russian ally, are strained.

Ukraine and the West accuse China of enabling the Russian invasion through trade and of supplying technology, including for deadly drone attacks.

Ukraine also says dozens of Chinese citizens have been recruited by Russia's army and sent to fight.

Ukraine's SBU security service said Wednesday the son was a 24-year-old former student of a technical university in Kyiv, and that the father, who lives in China, had travelled to Ukraine to coordinate his son's "espionage activities".

The two were "attempting to illegally export secret documentation on the Ukrainian RK-360MC Neptune missile system to China," the agency said.

Moscow and Beijing struck a "no limits" partnership on the eve of Russia's February 2022 invasion, and have since deepened political, military and economic cooperation.