MANILA - A unit of the Philippines' Philex Petroleum Corp. wants to do more drilling around a natural gas field in contested waters in South China Sea despite a deepening diplomatic dispute between Manila and Beijing over the area.

London-listed Forum Energy Plc., which is majority-owned by Philex, plans this year to conduct a survey to identify and evaluate other gas prospects near its Sampaguita gas field in the Reed Bank, where the Philippines is spending millions to harden its military presence.

Territorial disputes between the Philippines and China have hampered Forum's plan to drill at least two more appraisal wells within the Service Contract 72 exploration permit awarded to it by the Philippine government in 2010.

In March 2011, two Chinese vessels threatened to ram a survey ship contracted by Forum in the Reed Bank area, triggering renewed tensions between the two countries. China lays claim to virtually all the South China Sea while the Philippines and four other countries - Brunei, Malaysia, Taiwan and Malaysia - claim certain parts.

"A seismic reprocessing program is being planned in 2013 to further assess the prospectivity of other areas outside the Sampaguita field within SC 72," Forum said in a filing linked to a Philex disclosure on Thursday to the Philippine Stock Exchange.

China says it owns the Reed Bank, but the Philippines insists it has sole sovereignty over the waters within its 200-mile exclusive economic zone.

"We remain in close dialogue with the Philippine government on how best to progress the development of this important asset," Forum said.

The South China Sea holds around 11 billion barrels of oil and 190 trillion cubic feet (tcf) of natural gas in proven and probable reserves, surpassing untapped resources in Europe, according to the U.S. Energy Information Administration.

The Philippines' Defense Department said on Thursday it will open tenders next month for P979 million ($24 million) worth of radars, sensors and weapons for two coastal watch stations on the western Palawan islands to help secure oil and gas exploration in the Reed Bank.

Fernando Manalo, defense undersecretary for finance, munitions, installations and materiel, told reporters the Philippines also wants to buy inflatable boats, small guns, and night vision goggles.

Sources in the Defense Department familiar with the project said four coastal radar stations will be set up on Palawan. A bid document on its website says the equipment is "for the enhancement of maritime domain awareness and security of the Department of Energy service contract areas."