The world has seen China become "more aggressive" during the COVID-19 pandemic, US Defense Secretary Mark Esper has said, asserting that the country has deployed troops along the Line of Actual Control with India and is acting out in a way that is "inconsistent" with international norms.

Esper said Beijing was trying to use the coronavirus tragedy to their advantage for "propaganda purposes".

"What we have seen with regard to what happened in the last seven months coming as part of COVID, if you will, we've seen China become more aggressive, trying to use the tragedy, of COVID-19 to their advantage for propaganda purposes. They have really overplayed their hand and we've seen them continue to try and exercise this muscle in the South China Sea," he said on Wednesday.

Beijing claims almost all of the 1.3 million square mile South China Sea as its sovereign territory. China has been building military bases on artificial islands in the region also claimed by Brunei, Malaysia, the Philippines, Taiwan and Vietnam.

Beijing has impeded commercial activity like fishing or mineral exploration by countries like Vietnam and the Philippines, claiming that the ownership of territory belonged to China for hundreds of years.

Responding to a question during Aspen Security Forum discussion, Esper said that the Chinese sank a Vietnamese fishing vessel a few months ago.

"They continue to twist the arms of others. They've deployed troops along the line of actual control in India. We see them acting out in a way that is inconsistent with, you know, international norms, rules of behaviour, if you will, and many of our allies and partners are reacting as well," he said.

His remarks came amid the border face-off between India and China in eastern Ladakh.

Twenty Indian army personnel were killed during the clashes with Chinese troops in eastern Ladakh's Galwan Valley on June 15. The Chinese side also suffered casualties in the clashes but it is yet to give out details.

The number of casualties on the Chinese side was 35, according to a US intelligence report.

The Defense Secretary praised Australia and the UK for pushing Huawei out of their systems or lauded the Australians for a brand-new defense strategy that has long-term commitment to funding.

According to Esper, the best way to take on the Chinese aggression is to multilateralise efforts against Beijing.

"...The US being unable to travel, we found new ways to communicate and to do it in a multilateral way. We need to continue to advance that. We need to multilateralise those. Maybe not officially, right? But in terms of knitting things up so we talk more as a group," he said.

"That's the best way to push back against China and its bad behaviour in the Pacific. And I see that as another positive outcome, if you will, of us being unable to travel. We found new ways to communicate and to do it in a multilateral way, and I think we need to continue to advance that," Esper said.

The threat posed by China is not region, but global, he said.

"The China competition, by the way, is not limited to Indo PACOM, it is a global competition so we see them in all parts of the world. So it's multifaceted and it requires tough decisions and look, we are making those tough decisions as best we can," Esper said.

Responding to another question, Esper said that he did not see China right now as an inevitable threat that the US is going to have a fight with.

"But we do have to compete, and we have to be much more vigorous in all domains if you will whether it's again diplomatic, informational, military, political,' he said.