A senior Pentagon official said that China continues to engage in dangerous acts that could lead to a military clash in the Indo-Pacific region with the U.S. amid an ongoing refusal to communicate.

Ely Ratner, the U.S. assistant secretary of defense for Indo-Pacific security affairs, made the remark at a forum hosted by the Washington-based Center for a New American Security on Thursday.

Ratner assessed that there has been a drastic increase in the Chinese military's active, offensive, unprofessional, dangerous and unsafe activities in the region during the past 18 months.

Criticizing past flights by Chinese jets that came dangerously close to U.S., Australian and Canadian patrol planes over the South China Sea and the Taiwan Strait, the official said the risky moves could lead to a crisis or a clash.

Ratner said communication with the Chinese military has become more difficult in the past six months, adding that the Chinese side has either refused or canceled dialogue at all levels.

He then stressed that Washington will be neither restrained nor threatened by such acts, but will continue to safely and responsibly operate in international airspace and waters in accordance with international laws.

The U.S. official added that as an important part of the National Defense Strategy(NDS), the U.S. has been modernizing its nuclear forces and strengthening the extended deterrence in preparation for the advancement of the nuclear capabilities of China and North Korea.