BRUSSELS — US Air Force Secretary Deborah Lee James, citing threats across the spectrum, has urged European allies to boost defense spending.

Speaking here in Brussels on Wednesday, she urged an increase in spending by all NATO members, calling on each to share the burden of tackling a whole range of threats ranging from Russian "aggression" and the and Islamic State to Chinese cyberspace hackers and health crises such as Ebola.

Mrs James said, "l firmly believe NATO can continue to be a force for peace and stability in Europe but we have to understand that peace and stability does not come free," James said.

"This is why we must invest in our security, both as individual nations and regions, like the EU."

The UK government has been criticized over its failure to meet NATO guidelines and commit to spending 2 percent of its GDP on defense beyond the end of this financial year.

While not naming any NATO or EU members, in particular, Mrs James urged NATO members to resist pressure to cut defense spending, adding, "Indeed, rather than cutting defense budgets, I would argue that spending should be increased."

James, responsible for a budget of more than $139 billion, US dollars, was in Brussels as part of a whistlestop European tour that included the Paris Air Show and concludes with a visit to Poland on Thursday.

She told a debate co-hosted by the US missions to the EU and NATO that, "I am all too aware that we all have continuing budgetary challenges and this is no different in the United States. But the security challenges facing us today, both externally and internally, means that we cannot take our security for granted. That is why we have to come together and continue to invest in defense."

She said the trans-Atlantic relationship is "more relevant than ever" but cautioned that NATO stood at a "crossroads."

She told a packed audience of military experts and EU policymakers, "The security threats we face are more sophisticated and diverse than ever and that is why we need credible armed forces with the means to defend our interests. But, and I repeat, security does not come for free."

The official would not be drawn on whether UK defense cuts may affect how Britain interacts with the US, but said that generally, "It is very important we stop this downtrend trend [in defense spending] and strive for the 2 percent target that I would remind you all NATO members agreed to."

A central outcome of the NATO summit in Wales last September was a promise for all European allies to recommit to spending 2 percent of their GDP on defense. - a long-standing obligation.

Cautioning against the potentially "devastating" consequences of further cuts among the allies, she said, "Defense spending really should be a red line and this is the path we are taking in the United States.

"I do not want further cuts but , rather, would rather that we move in an upwardly direction when it comes to defense spending. That is what I think we should all be striving for."

She reminded the audience that Russia had increased military spending as it renews levels of tension with the West not seen since the Cold War, and the appearance of ISIS.

On Russia, she condemned its "illegal occupation" of Crimea and accused it of "fueling" the conflict in East Ukraine.

"Russian aggression is a blatant challenge to the accepted norms and it is deliberately creating a thick fog of confusion in order to try and obscure what is going on in Ukraine," she told the 60-minute debate.

She added, "We want to be a good partner for all countries but there are international standards of behavior and when these are broken we cannot just continue as if it was business as usual."

James, who is the 23rd US Air Force secretary who of the United States Air Force and has 30 years of senior homeland and national security experience, also called for "patience" in tackling the threat posed by Islamic State.

"The solution cannot be a military one alone and this is going to take time. It is a work in progress."

On the trans-Atlantic relationship, she said, "To those who say that it is in decline or on the wane I say, I do not believe that one bit.

"Security-wise, there is a lot on our plate and demand is growing because global challenges are moving at a dizzying pace. The threats are greater than ever and no one nation can meet these challenges on are their own.

"The presence of thousands of US Air Force men and women in Europe demonstrates our longstanding commitment to Europe. There is no doubt that we see Europe as our oldest and most trusted partner."

This partnership extended to space, she argued, saying that what was once a "peaceful domain" (space) was now the source of potential conflict, including militarily.

"Space today is contested and congested," she added.

When it comes to predicting future threats, James conceded it was impossible to forecast where the next security challenge may come from, adding, "That is why we need what I call a strategic agility."