Manila and Beijing traded accusations about a maritime confrontation Wednesday around the disputed Scarborough Shoal, a day after China submitted a chart of the South China Sea feature’s shore to the U.N. to bolster its claim over it.

Tensions flared once again in the South China Sea this week as the coast guards of China and the Philippines offered conflicting accounts of a maritime confrontation near the contested Scarborough Shoal.

China has blocked four Philippine vessels that attempted to “intrude into the territorial waters” of the disputed Scarborough Shoal on Wednesday, the country’s coastguard said.