Malaysia’s push to explore energy blocks off its coast has turned into a five-nation face-off involving U.S. and Chinese warships, raising the risk of a direct confrontation as broader tensions grow between the world’s biggest economies.

The episode began in December, when Malaysia’s state-run energy giant Petroliam Nasional Bhd. contracted a vessel to explore two areas in the South China Sea in its extended continental shelf. Those waters are also claimed by Vietnam and China, which immediately sent ships to shadow the boat.

The situation took a turn for the worse on April 16 with the arrival of a Chinese surveyor known as the Haiyang Dizhi 8, which last year was engaged in a standoff with Vietnam over offshore energy blocks. The U.S. this week sent at least two warships within some 50 nautical miles of the Malaysian ship, according to defense analysts privy to the information who asked not to be identified.