The United States frequently sending military vessels and aircraft to the South China Sea for muscle flexing is the root cause for maritime security issues and disruption of regional peace, Foreign Ministry spokesman Guo Jiakun said on Monday.

Guo made the remarks at a regular news conference, after reports said a fighter jet and a helicopter of the US Navy crashed in the South China Sea in separate incidents on Sunday.

The aircraft crashed during a military drill in the region, Guo said.

"If the US requests, China is willing to provide necessary assistance to the US out of humanitarianism," Guo said.