ASPEN - US Treasury Secretary Jack Lew has said he will keep up pressure on China over cyber security, especially stealing of intellectual property and trade secrets, which he sees as separate from other Internet-related issues between the two countries.

The recently appointed Treasury secretary said on Sunday he had already raised his concerns on cyber security when he met with Chinese President Xi Jinping in China recently.

"It is fundamentally a different set of issues and is something that is going to remain high on our agenda of issues to talk to with them about," he told an audience at the Aspen Ideas festival, saying the meetings in China were "productive."

Lew and Secretary of State John Kerry are set to host their Chinese counterparts in Washington DC next week for the annual US-China Strategic and Economic Dialogue.

Computer hacking is a contentious issue between the two countries. US intelligence leaders have said that cyber attacks and cyber espionage had supplanted terrorism as the top security threat facing the United States.

For its part, China accused US recently of "double standards" in cyber security after the flight from Hong Kong of fugitive former spy agency contractor Edward Snowden, who leaked details of US cyber surveillance tactics.

While not directly referring to the Snowden issue, Lew said cyber theft "is just different from other kinds of issues in the cyber area".

Lew said he also used the recent visit to Beijing to try and convince the new Chinese administration to reduce barriers to trade and open up the country to wider foreign investment.

US companies face barriers to invest in around 100 Chinese sectors, while China holds that US bars Chinese investments on unjustified national security grounds.

"They fundamentally have to move from a place where they have a very rigid, structured support for all the industries and go to more market-determined interest rates, market-determined investment policies, opening their market more to international investment," Lew said.

"The fact that there are other issues that do come up between us can't become an issue as we talk about the core economic issues which are frankly things China needs to do in order to grow its economy," he added.