An aerial view of China-occupied Subi Reef at Spratly Islands in the disputed South China Sea. REUTERS/Francis Malasig/Pool

MANILA (Reuters) - The Philippines has completed an 18-day scientific survey in the South China Sea to assess the condition of coral reefs and draw a nautical map of disputed area, a top security official said on Thursday.

Two survey ships, including an advanced research vessel acquired from the United States, conducted surveys around Scarborough Shoal and on three islands, including Thitu, in the Spratly group, National Security Adviser Hermogenes Esperon said.

“This purely scientific and environmental undertaking was pursued in line with Philippine responsibilities under the U.N. Convention of the Law of the Sea to protect the marine biodiversity and ensure the safety of navigation within the Philippines’ EEZ,” Esperon said in a statement.

He gave no details of the findings from the reef assessments and nautical mapping of the area done from April 7-25.

China claims almost the entire South China Sea, but it appeared to have allowed the survey. Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims in the strategic waterway.

Other countries in the region were regularly making scientific surveys in the area, said a navy official who declined to be named.

The navy official told Reuters the Philippines also conducts marine survey from time to time, but this was its first major undertaking since 2011, when a Chinese patrol boat harassed a survey ship hired by an Anglo-Filipino company to explore for oil and gas in the Reed Bank.

Esperon said researchers from the environment ministry, the country’s premier university and the navy took part in the expedition.

“This is the first leg of the expedition,” he said, adding the government also plans to conduct research in Benham Rise, part of the Philippines’ continental shelf, in the Pacific Ocean.