Defense Secretary Lloyd Austin said it was "unfortunate" China declined a US offer to speak at a defense summit this week in Singapore and that the ongoing lack of communication could result in "an incident that could very, very quickly spiral out of control."

"(Y)ou've heard me talk a number of times about the importance of countries, with large, with significant capabilities, being able to talk to each other so you can manage crises and prevent things from spiraling out of control unnecessarily," Austin said at a news conference Thursday in Japan with Japanese Minster of Defense Yasukazu Hamada.

"And as we take a look at some of the things that China is doing in the international airspace in the region and international waterways, you know, the provocative intercepts of our aircraft and also our allies' aircraft, that's very concerning, and we would hope that they would alter their actions. But since they haven't yet, I'm concerned about, at some point, having an incident that could very, very quickly spiral out of control," Austin said, adding that he would "welcome any opportunity to engage" with China's leadership.

The Pentagon said earlier this week that China refused a US proposal for Austin to meet with his Chinese counterpart Li Shangfu at the Shangri-La Dialogue security forum in Singapore this week. China's defense ministry blamed the US for their refusal, saying the responsibility for ongoing tension between the two countries' militaries "lies entirely with the US side."

The comments come as Chinese President Xi Jinping told China's national security officials to think about "worst case" scenarios and prepare for "stormy seas," as the ruling Communist Party hardens efforts to counter any perceived internal and external threats.

Relations between the two countries have been increasingly strained in recent months, especially after former House Speaker Nancy Pelosi's trip to the self-governing island of Taiwan last August and the US' decision to shoot down a Chinese spy balloon that transited over sensitive US military sites in February.