China is demanding that the Philippines release fishing boats it said were seized by the Philippine navy after a collision in a disputed area of the South China Sea.

The demand Thursday comes one day after the Philippines issued a formal apology for the incident. Manila called the collision near the Spratly islands an accident and blamed it on steering problems with one of its warships. The apology made no reference to any boat seizures.

Thursday, Chinese Foreign Ministry spokeswoman Jiang Yu said the presence of Chinese fishermen near the Spratlys was fully justified in an area fished by Chinese mariners for generations.

The Philippine government said Wednesday a Chinese fishing vessel had intruded into its territorial waters and that one of its navy ships accidentally collided with a dinghy that the Chinese vessel was towing.

China, the Philippines, Vietnam and three other Southeast Asian nations all claim sovereignty over all or part of the Spratlys, which is thought to be rich in oil and mineral deposits. Beijing threatened earlier this year to use military force to protect its claims to virtually all of the sea. But it later pledged to work with Vietnam to find a peaceful solution.