A recent spate of dangerous midair encounters between American military aircraft and Chinese and Russian planes in the Pacific is the result of increasingly assertive strategies by both U.S. adversaries to project power far beyond their borders, according to the top U.S. Air Force commander in the region.

Air Force Gen. Herbert “Hawk” Carlisle, the head of U.S. Pacific Air Forces, said China’s naval and air forces in particular are “very much continuing to push” and becoming more active in international waters and airspace in Asia.

“They still talk about the century of humiliation in the last century. They still talk about this as the rise of China,” Carlisle said in an interview. “They still talk about this as their great nation. And they want to continue to demonstrate that.”

Carlisle said U.S. and Chinese forces are frequently encountering each other in parts of the East China and South China seas where they rarely came into contact in the past. Since commissioning its first aircraft carrier two years ago, China’s navy has conducted more exercises farther away from its shores and is closely patrolling areas in disputed waters where Chinese companies are drilling for oil.

Those movements have prompted the U.S. military in turn to deploy its ships and reconnaissance aircraft to keep a close watch. China’s military usually responds by conducting intercepts of U.S. aircraft as the two sides jockey for position, Carlisle said.

“All of that makes their tension go up a little bit,” he added.

U.S. officials said one such encounter got out of hand in August, when a Chinese J-11 fighter jet flashed past a Navy Poseidon P-8 patrol aircraft, performing a “barrel roll” at close range and bringing its wingtip within 20 feet of the U.S. plane. That incident occurred in international airspace about 135 miles east of China’s Hainan Island.

At the time, Pentagon officials protested publicly and released photos of the near-miss, which they cited as evidence of rash and irresponsible behavior on the part of the Chinese pilot. They said the same Chinese military unit had conducted three other risky intercepts of U.S. aircraft earlier in the year.

Carlisle was more measured in his assessment, saying that there has always been “an ebb and flow” in the number of Chinese intercepts and that he didn’t think China’s military leadership was looking to provoke a conflict.

“I personally don’t think it needs to get too much hype,” said Carlisle, who will leave his post in the Pacific this month to take a new assignment as chief of the Air Force’s Air Combat Command at Joint Base Langley-Eustis in Hampton, Va. But he acknowledged that “the opportunity for something to go wrong” will likely increase as China’s military gathers strength and moves farther afield.

To prevent such incidents, the Pentagon has tried to enhance communications channels and expand formal ties with the People’s Liberation Army in recent years. Although U.S. officials said progress has been made, they added that they didn’t expect to solve the issue overnight.

“I am disappointed. Am I surprised? I’m not necessarily surprised,” Adm. Samuel Locklear, the chief of the U.S. Pacific Command, said at a Sept. 25 news briefing at the Pentagon, when asked about the close calls. He added that the “vast majority” of interactions between U.S. and Chinese military aircraft and ships resulted in no problems. “It’s those outliers that concern us.”

While the Pentagon has long expected an increase in Chinese military activity in the Pacific, it has also had to confront a resurgent Russia, which is conducting more long-range reconnaissance and bomber missions in the region and even approaching U.S. territory.

On Sept. 17, U.S. fighter jets intercepted a half-dozen Russian military planes — two fighter jets, two long-range bombers and two refueling tankers — as they were flying in international airspace near the coast of Alaska. U.S. officials said they have also seen an increase in Russian bombers flying near Guam, the U.S. territory in the Pacific.

Carlisle attributed the Russian flights to a strategy by President Vladi­mir Putin “to reassert Russia into what he thinks its rightful place in the international order is, and part of that is continuing to push into the Pacific.”

He described the Russian maneuvers as “a little harder to figure out” in comparison with Chinese military actions, which he called “more rational.”

Russia has also become more active in airspace between its Pacific border and Japan, prompting a sharp rise in Japanese intercepts of Russian military aircraft over the past year.

In turn, Russia hasn’t hesitated to challenge U.S. reconnaissance flights near its territory. In April, a Russian Su-27 fighter jet flew within 100 feet of a U.S. Air Force RC-135U aircraft that was operating in international airspace over the Sea of Okhotsk, prompting complaints from the Pentagon.