BEIJING (AP) — Chinese patrol boats confronted Japanese vessels near a disputed East China Sea archipelago early Tuesday, the latest in a series of such encounters following Tokyo’s nationalization of the islands last month.

Four ships from China Marine Surveillance entered waters near the islands at 10 a.m. (0200 GMT), according to a statement from the State Oceanic Administration that commands the service. The ships conducted surveillance on the on Japanese Coast Guard vessels in the area, “sternly expressed” China’s sovereignty claim over the islands and “carried out expulsion measures,” the administration said.