Vice Foreign Minister Funakoshi Takehiro summoned Wu Jianghao Sunday afternoon and "made a strong protest that such dangerous acts are extremely regrettable", the ministry said in a statement.

Funakoshi "strongly urged the Government of China to ensure that similar actions do not recur," it said late Sunday.

Chinese military aircraft twice locked radar onto Japanese fighter jets southeast of Okinawa's main island on Saturday, Japan's defence ministry said.

Fighter jets use their radar for fire control to identify targets as well as for search and rescue operations.

Japanese Defence Minister Shinjiro Koizumi on Sunday said the incident was "dangerous and extremely regrettable".

The Chinese navy said Tokyo's claim was "completely inconsistent with the facts".

Beijing-Tokyo relations have soured over the past month, following remarks by Japanese Prime Minister Sanae Takaichi suggesting that Tokyo could intervene militarily in any attack on Taiwan.