Ahead of joint military drills by the Philippines and the United States next week, China urged the Philippines on Wednesday to refrain from bringing countries outside the South China Sea into regional issues.

"The Philippines should understand that drawing in countries outside the South China Sea to flex their muscles and stoke confrontation in the region will only intensify tensions and undermine regional stability," Foreign Ministry spokesman Lin Jian said.

Philippine and US forces will simulate "retaking" islands during the annual Balikatan drills running from Monday to May 10, which will involve 16,700 soldiers, Reuters reported.

"By trying to introduce external forces to maintain its so-called security, the Philippines will only put itself into greater insecurity, and even become the pawn of others," Lin said at a regular news conference in Beijing.

Following a US-Japan-Philippines summit in Washington last week, leaders of the three countries issued a joint statement in which they attacked China with regard to the South China Sea issue.

At a forum in Manila earlier this week, Philippine President Ferdinand Marcos Jr said the US-Philippines mutual defense treaty could be invoked "if any… Filipino serviceman is killed by an attack from any foreign power".

Lin urged the Philippines to stop making provocations at sea, and called on countries outside the South China Sea to stop stirring up confrontation in the region.

"China will continue to take necessary measures, firmly protect its territorial sovereignty and maritime interests, and maintain peace and stability in the South China Sea," he said.