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. Australia will receive assistance from the U.S., U.K., and Canada in its acquisition of nuclear-powered submarines. This will enable the Australian navy counter-attack Chinese-powered vessels.

They downplayed any notion that this partnership was aimed 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.

He stated that China is the regional strategic problem.

I’m certain Beijing won’t like this development, but what can they expect? It is obvious that all the countries of the region, including China’s, will want to become stronger to counter an aggressive China. That’s exactly what this announcement has done.

China’s Washington embassy spokesperson Liu Pengyu stated to Reuters that the countries should not create exclusionary blocs which target or harm the interests of third parties in response to the security pact. 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 used it as a tool in the past to penalize Australia. There are many other options China has. 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.

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

Jennings suggested that the Indo-Pacific region should have a strong “deterrence impact” so that China can conclude it is not worthwhile to pursue a military campaign against Taiwan.

The Taiwan Strait is the only thing that separates Taiwan from mainland China. It measures approximately 100 miles (160km) in 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 is asserting its claim to Taiwan more aggressively, with numerous Chinese warplanes breaking into Taiwan’s air defence zone this year.

Jennings stated, “Frankly, if the U.S. and the U.K. have an alliance relationship that is more powerful than before, that paints a picture that says to China, ‘You won’t get away from attacking Taiwan the same way you got away militarizing the South China Sea.'”

According to reports, the South China Sea is an important commercial shipping route and waterway that’s rich in resources. It also hosts trillions of dollars worth of trade each year.

Beijing has claimed almost all of the sea and built military outposts on artificial island that it constructed in these waters. Many Asian countries, such as Vietnam, Malaysia and the Philippines claim certain parts of South China Sea to be their territory.  

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.