BEIJING - The drilling activities of China Oilfield Services Limited (COSL) are located only 17 nautical miles (some 31 kilometers) from China's Zhongjian Island, completely within the country's territorial waters, an official has said.

Yi Xianliang, Deputy Director-General of the Department of Boundary and Ocean Affairs of the Foreign Ministry of China, told reporters on Friday that the Chinese side was "deeply surprised and shocked" by Vietnam's intensive attempts since May 2 to disrupt the Chinese company's normal drilling activities in the waters off China's Xisha Islands.

The Xisha Islands are an inherent part of China's territory and there is not any dispute about it, said the official.

The operations undertaken by COSL are only 17 nautical miles from Zhongjian Island, while they are as far as 130-150 nautical miles (241-278 kilometers) from Vietnam's coastline, he said.

Yi said Chinese enterprises started operations in the area ten years ago and in the time period from May to June 2013, a Chinese company carried out three-dimensional seismic operations there as well.

The ongoing operations are a normal follow-up to those past operations, he added.

Yi said the Chinese company's operations are completely within the mandate of China's sovereignty, sovereign rights and jurisdiction, and that Vietnam's harassment of the company's normal activities has seriously violated China's sovereignty, sovereign rights and jurisdiction, and gravely affected the production and safety of China's drilling rig.

It has caused unnecessary trouble for the China-Vietnam relationship, he added.

Faced with the harassment, the Chinese side had to strengthen security on the spot to stop the Vietnamese side's behavior and ensure the operations as well as navigation security.

"We demand the Vietnamese side sincerely respect China's legitimate rights, return to a rational track, immediately stop all forms of harassment and withdraw all its vessels and personnel from the area," said the Chinese official.