The NSA whistleblower Edward Snowden vowed on Wednesday to fight any move by the US to have him extradited from Hong Kong, saying he was not there to "hide from justice" and would put his trust in its legal system.

In his first comments since revealing his identity in the Guardian at the weekend, Snowden also claimed that the US had been hacking Hong Kong and China since 2009, and accused the US of bullying the territory to return him because it did not want local authorities to learn of its cyber activities.

As a debate raged over whether Snowden should be praised or prosecuted for his actions, he told the South China Morning Post: "I'm neither traitor nor hero. I'm an American."

Snowden claimed that the US had hacked hundreds of targets in Hong Kong – including public officials, a university, businesses and students in the city – and on the mainland. These were part of more than 61,000 NSA hacking operations globally, he alleged.

"We hack network backbones – like huge internet routers, basically – that give us access to the communications of hundreds of thousands of computers without having to hack every single one," he said.

The Post said it had seen a document that, Snowden alleged, supported his claims. The Post said it had not verified the document, and did not immediately publish it.

Snowden said he was releasing the information to demonstrate "the hypocrisy of the US government when it claims that it does not target civilian infrastructure, unlike its adversaries".

A senior Chinese official said last week he had "mountains of data" on cyber-attacks from the US, after Washington turned up the pressure over hacking by China.

Jen Psaki, a spokeswoman for the State Department in Washington, said it was not aware of the hacking claims and could not comment directly, but she rejected the idea that such an incident would represent double standards given recent US criticism of Chinese cyber attacks.

"There is a difference between going after economic data and the issues of surveillance that the president has addressed which are about trying to stop people doing us harm," she said.

Snowden, 29, was a computer technical assistant working for Booz Allen Hamilton, on contract to the National Security Agency (NSA). He left his job and home in Hawaii in May, set up camp in Hong Kong and provided the Guardian with top-secret documents that led to a series of revelations about the extent of US surveillance last week. For three weeks, he stayed in a hotel in the Kowloon district. But after identifying himself as the whistleblower in a video posted by the Guardian on Sunday, he felt he needed to move to a more secure location, and checked out on Monday.

Hong Kong appeared a strange choice for Snowdon, as it has a surrender treaty with the US and leans towards co-operating with US requests. But in his hour-long interview, Snowden told the South China Morning Post: "People who think I made a mistake in picking Hong Kong as a location misunderstand my intentions. I am not here to hide from justice. I am here to reveal criminality."

He added: "My intention is to ask the courts and people of Hong Kong to decide my fate. I have been given no reason to doubt your system."

Although China has had sovereignty over Hong Kong since 1997, the territory retains a separate legal system and tradition of free speech. Beijing normally does not become involved in surrender hearings – technically not extradition, as Hong Kong is not a sovereign state – but could make an exception given the high-profile nature of this case.

Even some human rights groups have questioned why he chose Hong Kong, given its control by China. But Snowden added: "I have had many opportunities to flee HK, but I would rather stay and fight the United States government in the courts, because I have faith in Hong Kong's rule of law."

The Hong Kong government has made no comment yet about the case. The chief executive of the Hong Kong government, Leung Chun-ying, on a visit to New York, repeatedly refused to comment on the case in a Bloomberg Television interview.

Snowden may have opted to give the interview to the Post to help build up a case for his being allowed to remain in Hong Kong, where opinion is divided between those expressing support and those who would like him to leave. He is turning into a cause célèbre, with a demonstration in support of him planned for Saturday.

It would be difficult for the Hong Kong police to arrest him until such time as the US makes a request for his return, since he has committed no crime in the city. In theory, he could attempt to fly out of the city, but it is likely he would be prevented from boarding the plane.

Similarly, if he were to attempt to move to mainland China, it is likely he would be stopped at the border. In any case, Snowden told the Post that he planned to stay in Hong Kong until he was asked to leave.

In Washington, an outspoken Republican congressman, Peter King, called for the arrest of the Guardian columnist who led the reporting on the NSA leaks, Glenn Greenwald. King told Fox News that Greenwald's stories were "putting American lives at risk and clearly done to hurt Americans". In a statement, the Guardian said it was "surprised and disappointed" by the comments.

In a separate development, the British foreign secretary, William Hague rejected suggestions that US surveillance programs were being used by UK authorities to avoid local privacy laws and spy on British citizens. On a visit to Washington where he met the secretary of state, John Kerry, he said: "No two countries in the world work more closely to protect the privacy of their citizens than the United Kingdom and the United States."

Kerry said they both understood the "very delicate but vital balance between privacy and the protection of people in our country".

Additional reporting by Dan Roberts in Washington