SINGAPORE - There are generally two schools of thought about how best to deal with China when difficult or politically sensitive problems arise.

The first is the softly-softly approach, one that believes quiet diplomacy behind the scenes will "save face'' and in the process, produce an amicable solution.

The other course of action suggests, however, that only persistent and very public pressure will compel Beijing to sit up and take real action.

On the growing issue of trans-national cyber intrusions, the United States has undoubtedly decided to go the second route in a big way.

At the annual Shangri-La Dialogue on Saturday, US Defence Secretary Chuck Hagel delivered one of the most public warnings yet to Beijing about American concerns over alleged Chinese hacking attempts.

"The US has expressed our concerns about the growing threat of cyber intrusions, some of which appear to be tied to the Chinese government and military," Mr Hagel told a room packed with top defence officials from the region and beyond, including representatives from China's People's Liberation Army.

In recent weeks, the US media has also stepped up a steady drumbeat of stories about the threat from Chinese hackers.

The most prominent one was a Washington Post report this week which cited a classified section of an independent report that said Beijing had used cyber attacks to glean data from nearly 40 US weapons programmes and nearly 30 other defence technologies.

Chinese officials have repeatedly refuted these allegations, insisting that China is itself the victim of cyber attacks.

These flat denials just won't do it anymore for the Obama administration, if the very concerted public campaign being waged by the US on this issue is any indication.

Prior to his arrival in Singapore, Mr Hagel acknowledged that public pressure rarely resolves an issue on its own, but that the problem has gotten to the stage where it can't be soft-pedalled anymore.

"It's pretty hard to prove that (the cyber attacks) are directed by any specific entity,'' Mr Hagel told reporters travelling with him.

"But we can tell where they come from. And I think we've got to be honest about that. I think we've got to let people know that.''

Will this tactic work? More importantly, if the public warnings don't bring results, will the US take some form of retaliatory action in response to the alleged cyber attacks?

This will undoubtedly be among the key questions on the table when US President Barack Obama and his Chinese counterpart Xi Jinping meet for a rare presidential retreat in California next week.