Last week, Russian and Chinese warplanes and ships approached the “last line” as part of joint exercises that began Sept. 10. Eight Russian warplanes and four warships, including two submarines, took part in the maneuvers. Pentagon spokesman Maj. Gen. Pat Ryder told a news conference that there was no cause for concern because U.S. airspace was not violated.

“This is not the first time that we have seen such maneuvers by Russian and Chinese military near our borders, and we are closely monitoring their actions,” — Ryder noted, emphasizing that the United States is ready to quickly respond to any possible threats.

The North American Air Defense Command (NORAD) has been tracking Russian military aircraft operating in the Alaskan air defense zone. The aircraft have been seen daily since September 11, for four days in a row, at a rate of two aircraft per day.

The Pentagon assures that these exercises do not pose an immediate threat to U.S. security, but active Russian and Chinese activities in the region continue to be closely monitored. Such maneuvers increase tensions in the Alaska region, where U.S. military departments have become accustomed to periodic tests of their response system to possible airspace intrusions.

The United States has already declared its readiness to respond to such actions.

"We are also ready to respond to this," — Ryder threatened.