Chairman of the US Joint Chiefs of Staff General Mark Milley and Defence Secretary Lloyd Austin appeared before the House Armed Services Committee in their first testimony before Congress since Russia's invasion of Ukraine.

The two Pentagon leaders said the threats from both Russia and China remain significant, while they defended the US approach to the war and the flow of arms the US is sending to Ukraine.

Milley said that Russia's invasion of Ukraine is "the greatest threat to peace and security of Europe and perhaps the world" in his 42 years serving in the US military, but added it was "heartening" to see the world rally around Ukraine.

"The Russian invasion of Ukraine is threatening to undermine not only European peace and stability but global peace and stability that my parents and a generation of Americans fought so hard to defend," Milley said, reported CNN.

"We are now facing two global powers: China and Russia, each with significant military capabilities both who intend to fundamentally change the rules based on current global order," Milley added. "We are entering a world that is becoming more unstable and the potential for significant international conflict is increasing, not decreasing."

Lawmakers in both parties focused at the hearing on the weapons that were being provided to Ukraine, asking whether more could be done as Ukraine has continued to ask for additional capabilities.

"One of the biggest questions we're going to have in this committee is, 'How can we do more?'" House Armed Services Chairman Adam Smith, a Washington state Democrat, said at the top of the hearing. "How can we make sure we're doing absolutely everything we can to help them?"

Rep. Mike Rogers of Alabama, the panel's top Republican, said he would support the US setting up permanent bases in eastern NATO countries like Poland and the Baltics in order to deter Russia. Milley said that he would support establishing permanent bases but added that he thought US forces should rotate through them to create a deterrent without incurring the costs of moving family, establishing schools and other measures required when a permanent US base is established abroad.

"I believe a lot of our European allies, especially those such as in the Baltics or Poland or Romania or elsewhere, they are very, very willing to establish permanent bases," Milley said. "They'll build them, they'll pay for them, etc., for us to cycle through on a rotational basis. So, you get the effect of permanent presence of forces, but the actual individual soldiers, sailors, airmen or Marines are not permanently stationed there for 2-3 years."

Austin said that NATO was still discussing how it should bolster its permanent presence in eastern Europe. "If NATO deems that it's appropriate to change its footprint, then certainly we'll be a part of that," Austin said.

Several Republicans asked Milley and Austin whether the US failed in its efforts to deter Russian President Vladimir Putin from attacking Ukraine. Milley responded that he did not think Putin could have been deterred unless US forces had deployed from Ukraine -- a scenario he would have advised against had it been proposed.

"Candidly, short of the commitment of US military forces into Ukraine proper, I'm not sure he was deterrable. This has been a long-term objective of his that goes back years," Milley said. "I think the idea of deterring Putin from invading Ukraine, deterring him by the United States, would have required the commitment of US military forces, and I think that would have risked armed conflict with Russia, which I certainly wouldn't have advised."

Milley noted that sanctions "have a very poor track record of deterring aggression," but said they have succeeded in imposing significant costs to Russia for its aggression.

"The objective of the sanctions is to impose significant costs if he invaded, those significant costs, the sanctions in combination with the export controls, are breaking the back of the Russian economy as we speak," he said.

Austin later added that had the US "put forces into Ukraine to fight Putin, this would be a different story."

"But we made a decision that we weren't going to do that and we made the decision for the right reasons, and I support those decisions," Austin said, adding he did not want to speculate on what Chinese leaders might extrapolate from what's transpired in Ukraine as it related to Taiwan.

Milley defended the US military's policy requiring troops to receive Covid-19 vaccinations in response to several queries from Republicans questioning whether service members should be discharged for refusing to be vaccinated when Army recruiting numbers were down.

Milley noted that service members have to receive numerous vaccinations as part of joining the military, like an Anthrax vaccine, and said that the Covid-19 vaccine contributed to force readiness.

In a heated moment, Austin got into an argument with Rep. Matt Gaetz after the Florida Republican accused the Pentagon of being too focused on "wokeism" and not defense.

Austin charged that Gaetz appeared to be "embarrassed for his country" by questioning the US military's capability, and the two men shouted over one another at several points.

Gaetz charged that the Pentagon "got it wrong" by predicting that Russia would overrun Ukraine within days and that the Taliban would not take control of Afghanistan last year. "You totally blew those calls and maybe we would be better at them if the National Defense University actually worked a little more on strategy and a little less on wokeism," Gaetz said.

"Has it occurred to you that Russia has not overrun Ukraine because of what we've done and what our allies have done?" Austin asked. "Have you ever even thought about that?"