The Philippines has accused Chinese fishermen of dumping cyanide in waters around the Spratly Islands, a fiercely contested area in the South China Sea.

Manila described the alleged poisoning as an act of 'sabotage' on Monday, intended to 'kill local fish populations' and deprive Filipino troops stationed at Second Thomas Shoal of a crucial food source.

China dismissed the claim as a 'farce'. The allegation follows years of tense stand-offs and occasional violent confrontations between Philippine and Chinese vessels in the disputed waters.

The South China Sea is at the center of a territorial dispute between China, the Philippines, and other countries. Chinese foreign ministry spokesman Guo Jiakin said the accusation was 'completely unbelievable and not even worth refuting.' He added, 'the Philippines has illegally harassed Chinese fishing vessels engaged in normal fishing activities.'

The Philippine National Security Council (NSC) stated that the alleged poisoning commenced last year around Second Thomas Shoal, part of the Spratly archipelago in the South China Sea. The reef is home to a small Philippine military outpost aboard the BRP Sierra Madre, deliberately grounded to assert Manila's claim.

NSC assistant director-general Cornelio Valencia stated that the use of cyanide was intended to 'kill local fish populations, depriving Navy personnel of a vital food source'. He mentioned health risks posed to troops by contaminating water and fish and potential damage to coral reefs supporting the vessel's structure.

Manila raised the alleged poisoning with Beijing at recent talks, but no formal response was received. The navy and coastguard were ordered to increase patrols in the area.

Philippine Navy spokesman Rear Admiral Roy Vincent Trinidad indicated that troops had seized 10 bottles of cyanide from boats allegedly launched from Chinese vessels last year, and another attempt was observed recently.

Cyanide fishing, used to stun fish for the live reef trade, is illegal under Philippine law and banned across Southeast Asia due to its destructive impact on marine ecosystems.

The South China Sea, a vital shipping route home to essential fishing grounds for millions, is a battleground for overlapping claims by multiple countries including Vietnam, Taiwan, and Malaysia. China asserts comprehensive claims despite a 2016 tribunal ruling that favored the Philippines and found China's claims without legal basis, which Beijing rejects.

Both nations claim the Scarborough Shoal, which lies closer to the Philippines than to China. Tensions have heightened significantly over the past years, with the Philippines conducting joint maritime exercises with the US and Australia, which China criticized for raising regional tensions.