• An increasingly aggressive and assertive China contributed to the formation of a new trilateral security partnership among the U.S., the U.K. and Australia, said Peter Jennings, executive director of think tank Australian Strategic Policy Institute.
• Under President Xi Jinping, China has militarized the South China Sea, tightened controls over Hong Kong, threatened Taiwan and Japan, as well as economically punished Australia, said Jennings.
• It's important to build "a strong deterrence effect" in the Indo-Pacific region so that China would conclude that "it's just not worth pursuing a military game against Taiwan," he added.

An increasingly aggressive and assertive China contributed to the formation of a new trilateral security partnership among the U.S., the U.K. and Australia, a defense expert told CNBC.

The the new partnership, announced on Wednesday, seeks to strengthen stability in Indo-Pacific. The U.S. and U.K. will assist Australia in acquiring nuclear-powered submarines, which will allow the Australian navy to help counter Chinese nuclear-powered vessels in the region.

The three countries downplayed the notion that the partnership is aimed specifically at China.

"I can assure you that none of this would have gone ahead were it not for more aggressive and assertive policies being pursued by Xi Jinping over the last half decade or more," Peter Jennings, executive director of think tank Australian Strategic Policy Institute, told CNBC's "Street Signs Asia" on Thursday.

Under Xi, China has militarized the South China Sea, tightened controls over Hong Kong, threatened Taiwan and Japan, as well as economically punished Australia, added Jennings.

"China is the strategic problem in the region," he said.

"I'm sure Beijing will not like this development but what do they expect? It's obviously going to be the case that the consequential countries in the region will seek to strengthen themselves in order to deal with a more aggressive China, and frankly that's what happened with this announcement."

In response to the new security pact, China's Washington embassy spokesman Liu Pengyu told Reuters that countries "should not build exclusionary blocs targeting or harming the interests of third parties. In particular, they should shake off their Cold-War mentality and ideological prejudice."

Derek Grossman, senior defense analyst at RAND Corporation, said China could use unilateral economic sanctions as a response to the new security grouping.

"China has used that ... as a lever in the past to punish Australia when it sees fit. But there's lots of other things China can do as well. They can ramp up their military assertiveness in the South China Sea, in the East China Sea against Taiwan," Grossman told CNBC's "Capital Connection" on Thursday.

'Deterrence effect' in Indo-Pacific

Experts on geopolitics have said that Taiwan is one the most dangerous flashpoints in the strategic competition between the U.S. and China.  

Jennings said it's important to build "a strong deterrence effect" in the Indo-Pacific region so that China would conclude that "it's just not worth pursuing a military game against Taiwan."

Taiwan and mainland China are separated by the Taiwan Strait, which is only about 100 miles wide (160 km) at its narrowest point. The ruling Chinese Communist Party in Beijing has never controlled Taiwan, but it claims the island is a runaway province that must one day be reunited with the mainland — by force if necessary.

China has more aggressively asserted its claims over Taiwan, and there have been numerous breaches of Taiwan's air defense zone by Chinese warplanes this year.

"Frankly if we have the U.S., the U.K., Australia operating together in a more forceful type of alliance relationship ... that begins to paint a picture which says to China: 'You're not going to get away with an attack on Taiwan in the way that you did get away with militarizing the South China Sea'," said Jennings.

The South China Sea is a resource-rich waterway and a vital commercial shipping route where trillions of dollars of world trade reportedly passed through each year.

Beijing claims nearly the entire sea, and has constructed military outposts on artificial islands that it built in those waters. Several Asian countries including Vietnam, the Philippines and Malaysia also claim parts of the South China Sea as their territories.  

In 2016, a tribunal at the Permanent Court of Arbitration dismissed China's claim as legally baseless — a ruling Beijing ignored.

— CNBC's Abigail Ng contributed to this report.