A Chinese oil rig in the South China Sea that has been the source of tensions between China and Vietnam earlier this month has completed the first phase of drilling, the rig’s operator said, in a statement Tuesday.

The company, China Oilfeld Services Limited, said the rig has already moved to another site but that the rig will continue to explore for oil off the Xisha islands, China’s name for the Paracel islands in the South China Sea, Reuters reported. The rig was deployed earlier this month and COSL said drilling was scheduled to be completed in mid-August.

Relations between China and Vietnam grew shaky over the rig, as Vietnam claimed the $1 billion drilling platform was set up in an area of the South China Sea that Hanoi claims is on its continental shelf. But China says the entire South China Sea belongs to Beijing.

In Vietnam, riots against China were staged after the discovery of the drilling platform while the Vietnamese government also lodged a protest against Beijing's deployment of the oil rig.