The Ministry of National Defense expressed its firm opposition to frequent and close-in US reconnaissance activities against China on Monday after a top US navy admiral joined a seven-hour-long surveillance flight over the South China Sea at the weekend.

US aircraft have conducted frequent reconnaissance flights against China for some time, which has gravely undermined China-US mutual trust and China's security interests, and is highly likely to cause maritime and airborne incidents, the ministry's press office said.

The ministry made the remarks to China Daily after the US Pacific Fleet said on Sunday that the new commander of the fleet, Admiral Scott Swift, joined the surveillance mission on board a P-8A Poseidon plane on Saturday.

The US did not give any specific details, except that it was a routine flight to witness the full range of capabilities of the aircraft, a new spy plane that can be used for a range of undertakings.

Peace and stability in the Asia-Pacific region is in all parties' interests, said the ministry, urging the US to keep its promise of not taking sides over the South China Sea issue and make more efforts for regional peace and stability.

In May, Beijing called a P-8 surveillance flight carrying a CNN team over the South China Sea "irresponsible and dangerous".