The defence ministry said the vessel's activities are in line with international law, reported the Global Times, which is close to the ruling Communist party.
Reports in the US quoted the US Navy saying that a Chinese surveillance vessel had been found operating near the location of the Rim of the Pacific (RIMPAC) naval exercises, viewed by analysts as one step toward potentially repairing ties at a time of heightened US-China tensions.
Four ships of the People's Liberation Army Navy with an estimated 1,100 sailors on board -- a missile destroyer, missile frigate, supply ship and hospital ship -- are officially taking part in the RIMPAC exercises, which began last month.
But China and the US have found themselves increasingly at odds as Beijing seeks to assert its claim to disputed territory in the East and South China Seas and as Washington seeks to shore up its influence in the region.
China's dispatch of the surveillance ship is a reminder that relations remain fraught between the Asian giant and western superpower.
"The People's Liberation Army naval ships' operation in waters outside the territorial seas of other countries is in line with international law and international practice," the Chinese defence ministry statement said.
"The Chinese side respect the rights of maritime countries in accordance with international laws, but also wishes relevant countries could respect the rights Chinese ships are entitled to enjoy by law," it added.
US officials have affirmed that the ship is operating legally.
Previously, Washington has accused Beijing of harassing US ships operating in international waters of the South China Sea.
In 2009, tensions spiked after five Chinese ships surrounded and nearly collided with a US Navy surveillance ship in waters off south China, in one of the highest-level confrontation between both countries in recent years.
More recently, Washington last December issued a formal protest after the USS Cowpens warship was forced to manoeuvre to avoid a collision with a Chinese naval vessel in the same waters.
Beijing claims almost the whole of the South China Sea, even areas close to the coasts of other littoral states.