China's coast guard said on Wednesday that it monitored the Philippines delivering necessities to a vessel on Second Thomas Shoal in the disputed South China Sea — roughly a month after Manila accused Beijing of obstructing its resupply mission to the same shoal.

The China Coast Guard said the Philippine ship receiving the delivery was "illegally grounded" at the shoal, which China claims as its own territory along with almost all of the South China Sea. The Philippine military and coast guard did not immediately respond to a request for comment, Reuters reported.

Tension at the shoal has run high for weeks. On September 25, the Philippine Coast Guard accused China of obstructing a resupply mission, while China said the Philippines had ignored its warnings, prompting what Beijing called "on-site monitoring" and verbal warnings. Separately in September, a Chinese coast guard vessel rammed a Philippine boat on a refuelling mission near another shoal, according to the Philippine Coast Guard; China blamed the collision on Manila.

On Monday, the Philippine foreign ministry summoned China's ambassador to express its "serious concern and strong objection" about remarks by the envoy that it said conveyed a threat of the use of force. The Chinese diplomat said he disagreed that his remarks conveyed a threat.