That would be the next step,” Pentagon spokesman Colonel Steven Warren told reporters on Thursday.
US officials say American surveillance planes and naval vessels have not yet ventured within 12 nautical miles of the man-made islands–the standard territorial zone around natural land.
Washington does not recognize China’s sovereignty in the disputed areas and is weighing sending surveillance aircraft and warships to test its territorial claims.
The Pentagon’s announcement came as an American television crew picked up a tense radio exchange between a US surveillance plane and Chinese forces in the South China Sea.
A Chinese navy dispatcher reportedly made eight demands Wednesday that the US Air Force P8-A Poseidon aircraft leave the airspace over the artificial islands, CNN reported.
The aircraft passed over the Fiery Cross Reef, where China is reportedly building an airfield and other installations.
Observers warn that US actions could escalate the already-heightened tensions in the South China Sea, leading to a standoff that could undermine global shipping lanes.
A navy official told AFP that “it’s not uncommon” for China to issue warnings to the US aircraft as it sometimes sends military aircraft to visually identify American planes in the area.
Washington accuses Beijing of undergoing a massive “land reclamation” program in the South China Sea to extend its zone of influence in the region.
The Pentagon’s annual report to Congress this month cast China as a threat to regional and international peace and stability. It questioned the transparency of Chinese defense, cyber and space programs.
For the first time, a section was devoted to China’s building projects in the South China Sea, which it warned were expanding rapidly.
US officials say China has “reclaimed” about 800 hectares (2,000 acres) of dry land in the Spratly Islands, one of the disputed areas, which could be used for military purposes.
China has said it has “indisputable sovereignty over the Nansha islands and adjacent waters”, using its name for the Spratlys.
Earlier this week, China’s Foreign Minister Wang Yi told visiting Secretary of State John Kerry that Beijing would not back down on its construction projects that fall “fully within the scope of China’s sovereignty.”
“I would like to reaffirm that the determination of the Chinese side to safeguard our own sovereignty and territorial integrity is as firm as a rock,” he said.
President Xi Jinping also told Kerry that the US and China must handle disputes in a way that does not affect their relationship. “The broad Pacific Ocean is vast enough to embrace both China and the United States.”
Xi and Kerry discussed the importance of the Chinese leader’s trip to Washington as tensions threaten to overshadow the September visit.
China’s territorial claims in the South China Sea overlap with those of Brunei, Malaysia, Vietnam and Taiwan, and more specifically the Philippines.
The United States is treaty-bound to defend the Philippines in any possible conflict with China.