BEIJING (Reuters) - China on Saturday demanded that Taiwan release two mainland fishermen who have been detained after the island’s coastguard fired rubber bullets at them amid simmering tensions between the rivals.

The shooting put a new strain on ties between Beijing and Taipei which have cooled since Taiwan President Tsai Ing-wen of the independence-leaning Democratic Progressive Party took power last year, because she refuses to concede the self-ruled island is part of China.

Taiwan’s coastguard said in a statement a Chinese fishing vessel trespassed into Taiwan waters, refused to stop and resisted inspection.

The Chinese fishermen ignored radio warnings, the statement said, adding that Taiwan coastguard fired rubber bullets, hitting some of the fishermen in the legs, but did not cause major injuries.

China’s Taiwan Affairs Office said two Chinese fishermen were injured in the incident near Penghu, also known as the Pescadores, on Saturday morning, state news agency Xinhua said.

“This morning’s shooting incident which injured mainland fishermen arouses indignation,” Xinhua quoted An Fengshan, spokesman for the Taiwan Affairs Office, as saying.

“We demand the Taiwan side solemnly deal with this matter and immediately release the fishermen and (their) boat” An said.

Taiwan “must stop the practice of detaining mainland fishing boats for no reason at all,” he said, urging Taiwan to “respect the rights of mainland fishermen.”

Beijing has not ruled out resorting to military means to force the democratic island back to the fold if it formally declares independence.

Beijing and Taipei have been rivals since the Communists won the civil war on the mainland and defeated Nationalist forces who fled to the island.