China said on Tuesday that sincerity, rather than a nation's size, should be used to gauge how it justifies its actions.

The comment came after remarks by US President Barack Obama that "big nations should not bully smaller ones".

Foreign Ministry spokeswoman Hua Chunying said that of the 12 neighbors China has completed demarcation agreements with, five countries are smaller than the Philippines in size and 10 are smaller in population.

"This shows that a country's size does not matter regarding the issue. The key point is whether countries involved have the determination and sincerity to resolve disputes via talks and consultations," Hua said at a media briefing.

The Philippines has unilaterally initiated an arbitration case against China in the Permanent Court of Arbitration at The Hague over their disputes in the South China Sea.

Obama told an audience in Hanoi on Tuesday, "Big nations should not bully smaller ones and disputes should be resolved peacefully".

Hua called for countries outside the region to respect the efforts of those in the region to maintain peace and stability.

Tao Wenzhao, an American studies researcher at the Chinese Academy of Social Sciences, said the US sees China as its biggest threat, both at present and in the long term.

"The US aims to multilateralize, globalize and militarize the disputes in the South China Sea, making the situation an important measure to contain China," Tao said.

Obama said during his speech that the US "will continue to fly, sail and operate wherever international law allows".