Freedom of navigation in the South China Sea "has never been a problem" and related countries should do more to protect peace and stability in the region, Foreign Ministry spokesman Hong Lei said on Wednesday. Hong made the remarks in response to the United States' latest claim that China remains "aggressive" to vessels conducting oil and gas exploration in disputed waters in the South China Sea.

According to the Associated Press, Admiral Robert Willard, head of the US Pacific Command, said on Tuesday that the American military must be present in the South China Sea to ensure the security of the sea lanes crucial to international trade.

"In fact, freedom and safety of navigation in the South China Sea has never been a problem, and has never been affected by the South China Sea disputes. We hope relevant parties, including non-claimant states, do more things that are beneficial to regional peace and stability," Hong said at a regular news conference.

China, the Philippines, Vietnam, Malaysia and Brunei all have claims over some islands and waters in the South China Sea, and the US has increased its presence in the Asia-Pacific region, claiming that it has a national interest in the peaceful resolution of disputes in the South China Sea.

Willard told the Senate Armed Services Committee that China was less confrontational in 2011 in asserting its claims in the South China Sea than it was in 2010, when tensions rose between it and other claimant states, according to the AP.

But Willard said China continues to challenge vessels conducting oil and gas exploration within space that it claims as its own. "They remain aggressive."

He noted that the South China Sea carries some $5.3 trillion in regional commerce, $1.2 trillion of it American trade.

"The US military must be present there to ensure the security of those sea lines of communication," Willard said.

Hong said China's stance on the South China Sea issue is "consistent - not stronger or weaker".

"China has insisted on peaceful development and friendly nationhood policies, eyeing regional peace and stability, and solving disputes with relevant parties through friendly negotiations based on historical facts and international law," Hong said.

Hong said the crux of the disputes are claims over the territory of some islands and demarcation of some waters in the sea.

"No country including China has claimed sovereignty over the whole South China Sea. We don't know whether those who always make irresponsible remarks on this issue are doing it out of ignorance or have ulterior motives. We need to clarify it," Hong said.

In another development, the Philippines said on Wednesday it would push ahead with plans to expand oil and gas exploration in the disputed waters despite China's claim of the area, according to the AFP.

Philippine Energy Undersecretary James Layug said it was preparing to issue exploration licenses for 15 blocs, three of which were in the South China Sea.

Hong said on Tuesday that "it is illegal for any country, government or company, without the Chinese government's permission, to develop oil and natural gas in waters under Chinese jurisdiction".