A Filipino navy patrol ship was shadowed by Chinese forces near a disputed shoal in the South China Sea, sparking a fresh exchange of accusations and warnings between the countries on Tuesday.

Chinese and Philippine security officials gave conflicting accounts of Monday’s encounter near Scarborough Shoal.

China has surrounded the shoal with its navy and coastguard ships since a tense standoff with Philippine vessels more than a decade ago.

A rich fishing atoll and a safe mooring area during storms, the shoal, off the north-western Philippines coast, is one of most fiercely contested territories in the South China Sea, where Chinese and Philippine forces have faced off in recent months.

The frequent confrontations, which led to an October 22 collision of Chinese and Philippine vessels near another disputed shoal, have prompted the United States to repeatedly renew a warning that it is obligated to defend the Philippines, its oldest treaty ally in Asia, if Filipino forces, ships or aircraft come under an armed attack in the Pacific, including in the South China Sea.

Chinese air force Colonel Tian Junli, a spokesperson for the Southern Theatre Command of the People’s Liberation Army, said a Philippine warship trespassed into what he said were Chinese waters around Scarborough Shoal on Monday and was “tracked, monitored, warned and restricted” by the Chinese navy and air force for seriously violating “China’s sovereignty and international law”.

“We urge the Philippine side to immediately stop its infringement and provocation to avoid further escalation,” he said in a statement.

Philippine national security adviser, Eduardo Ano, however, said in Manila that the Philippine navy ship carried out a routine patrol of the waters in the vicinity of Scarborough “without any untoward incident”, but added that “Chinese vessels, as usual, conducted shadowing on the movement” of the Philippine navy ship.

Ano accused China of hyping up the encounter and “creating unnecessary tensions between our two nations”.

“The armed forces of the Philippines and the Philippine coastguard will not be deterred by the aggressive and illegal activities” of China’s navy, coastguard and militia forces, he added.

The territorial disputes in the South China Sea, which also involve Vietnam, Malaysia, Taiwan and Brunei, have long been feared as an Asian flashpoint and have become a delicate fault line in the regional rivalry between the US and China.