GUANGZHOU -- A China Marine Surveillance (CMS) patrol team recently finished its third mission targeted at the illegal exploration of oil and gas in the South China Sea, a maritime official said Monday.

The team included the Haijian 83 and Haijian 75 patrol ships from the South Sea fleet of the China Maritime Surveillance Force in the southern city of Guangzhou, said a source with the South China Sea branch of the State Oceanic Administration (SOA).

The team focused on searching for and monitoring illegal offshore oil and gas extraction platforms, discovering more than 30 illegal platforms in total, the SOA source said.

The CMS has been sending patrols to the South China Sea and other Chinese territorial waters since 2007.

The South Sea fleet of the China Maritime Surveillance Force has intensified its patrols in the South China Sea in recent years, conducting nearly three times as many missions in 2011 as it did in 2008.