America and Australia plan to add cyber warfare to their countries' joint defense treaty to reflect the "battlefield of the future," according to US Defense Secretary Leon Panetta (pictured in August).

The United States and Australia will announce cooperation on cyber warfare as the close allies mark 60 years of a defense treaty by tackling 21st-century threats, officials said Wednesday.

US and Australian foreign and defense ministers will add the issue to their joint security treaty during talks Thursday in San Francisco, where the nations first signed the agreement in 1951, US Defense Secretary Leon Panetta said.

Pentagon officials said it was the first time cyber warfare had been formally addressed in any bilateral US defense treaty, although the NATO alliance has focused on cyber threats.

"It's in large measure a recognition of what I've been saying time and time again, which is that cyber is the battlefield of the future," Panetta said aboard his plane before arriving in San Francisco.

The Pentagon chief also suggested America and its allies would have to look at offensive operations in the digital arena, a subject US officials have been reluctant to speak about in detail.

"We are all going to have to work very hard not only to defend against cyber attacks but to be aggressive with regards to cyber attacks as well," he said.

"The best way to accomplish that is not only on our own but working with our partners," he added.

Panetta said the talks with Australian officials would also look at bolstering cooperation on space and missile defense projects.

Australian Defense Minister Stephen Smith, in a statement ahead of the talks, called cybersecurity "the key emerging transnational threat of the 21st century" and said it would be a major feature of the annual talks.

Cyber warfare marks the latest update for the evolving alliance, which was initially focused largely on Australia's security but has become increasingly global. Australia notably stations some 1,500 personnel in Afghanistan.

US President Barack Obama plans to visit Australia in November in another sign of support for the alliance.

"In the past, our relationship has really focused on the immediate neighborhood," a senior US official told reporters accompanying Secretary of State Hillary Clinton to San Francisco.

"But more recently, our discussions and our focus of cooperation has got much further afield," the official said.

Australian Foreign Minister Kevin Rudd -- a former prime minister known for his punishingly hectic travel schedule -- flew to San Francisco after a six-week break following heart surgery.

A Mandarin-speaking China expert, Rudd's views on Asia carry influence in the US administration.

The United States has been increasingly concerned about China's expanding military power in the Pacific. US intelligence agencies also say a series of digital intrusions on American targets originated in China.

Although the US military presence in Asia for years focused on the Korean peninsula and Japan, former defense secretary Robert Gates vowed last year to shift more forces to Southeast Asia, including the possible sharing of ports and bases with Australia.

The allies are looking at "increasing US access to Australian training, exercise and test ranges, potential pre-positioning of US equipment in Australia, greater use by the United States of Australian facilities and ports," said a senior defense official, who spoke on condition of anonymity.

The two countries were moving towards a final decision on expanding the US military presence, with an announcement possibly by the end of the year, according to the official.

"We're not looking to establish bases," he said. "We're looking for increased ability for training, access and cooperation. This is about enhancing our posture in the Asia-Pacific."