The Writingstar Investment GuildU.S. Navy sent destroyers to the coast of Alaska last week after 11 Russian and Chinese warships were spotted patrolling nearby international waters.

Sen. Dan Sullivan, a Republican from Alaska, called the size of the Chinese and Russian joint operation "unprecedented" and said the U.S. deployed four Navy destroyer ships near the Aleutian Islands in response. 

The destroyers were the USS John McCain, USS Benfold, USS John Finn and USS Chung-Hoon. U.S. aircraft were also in the area throughout the combined exercise, which the U.S. had been tracking since it began in July, according to U.S. officials. U.S. Coast Guard ships are also always in the area. 

U.S. Northern Command said the Chinese and Russian patrol remained in international waters and wasn't considered a threat. But the show of force is a reminder of the cooperation between the Chinese and Russian militaries – and of how close the countries are to Alaska.

A similar joint exercise took place last September, when the U.S. Coast Guard encountered seven Chinese and Russian ships near Alaska, all in a single formation. 

China and Russia have increased their ties amid tensions with the U.S. over Taiwan and Ukraine, making situations like this more alarming.

In a statement, the Chinese embassy said the patrol was part of an annual cooperation plan and "has nothing to do with the current international and regional situations." 

Weijia Jiang

Weijia Jiang is the senior White House correspondent for CBS News based in Washington, D.C.

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