Chinese Ambassador to the United States Cui Tiankai said the strengthened U.S. military presence in the South China Sea has undermined the situation in the region.

"Actually, without outside interference, the situation in the region was cooling down, was quite stable," Cui said in an exclusive interview with Fareed Zakaria, host of CNN's GPS show, that was aired on Sunday, in response to U.S. accusations against China over the South China Sea.

"Unfortunately, countries like the U.S., particularly the United States, are trying very hard to intervene, to send their military, to strengthen their military presence in the region. The intensity and frequency is so high," he said.

"But ironically, the United States is not yet a contracting party to the Convention on the Law of the Sea. I don't know how many people are aware of this," Cui said.

The ambassador pointed out that the related ruling issued by a law-abusing tribunal in The Hague in July 2016 was "a unilateral action."

"We rejected it from the very beginning. We don't think this is the right thing to do. But some people insisted on doing it. We have told them very clearly at the very beginning that this is not the right thing to do. We will not participate in such a ruling. So it's not based on very solid legal ground," he said.

"But at the same time, we have a very strong position on our sovereignty, on the territorial claim in the region. Our claims have very strong historical and legal foundation," he said, adding that China wants to solve all the disputes with other countries through diplomatic negotiation.

Recalling his experience some years ago of working on the Declaration of Conduct between China and the Association of Southeast Asian Nations, Cui said:" Now we are working on the Code of Conduct, and we are making good progress."