It is also regularly crossing blocks 132 and 131 that Vietnam has licensed to Vietgazprom, a joint venture between Russia’s giant Gazprom and PetroVietnam. China has launched competing bids to licence those two blocks.
The three companies and the Russian embassy in Hanoi did not immediately reply to requests for comment.
On Thursday, when Vietnam issued a rare public statement demanding the ships leave, they were in block 129, also operated by Vietgazprom, according to Powell. The statement followed a visit to Hanoi on Monday by Russian former President and deputy chairman of Russia’s security council Dmitry Medvedev.
Two Vietnamese fisheries ships were on Friday shadowing the Chinese vessels at a distance of 200m to 300m, Powell said, noting the Chinese ships had moved to a block adjacent to those operated by Russian firms.
China claims most of the energy-rich waters of the South China Sea, including areas that are within Vietnam’s EEZ.
Under international rules, ships are allowed to cross other countries’ EEZs but China’s operations have long been perceived as hostile by Vietnam and other countries with claims in the South China Sea, including the Philippines and Indonesia.