Greens senator Peter Whish-Wilson said the comparison between Lei and Assange was drawn in several meetings in Washington last month to highlight the precedent that Assange's prosecution could set for countries like China.

Mr Whish-Wilson was part of a cross-party contingent of MPs and senators who headed to Washington to lobby members of Congress, the State Department and the Justice Department into stopping their pursuit of the Wikileaks founder.

Assange is currently in Belmarsh Prison in the United Kingdom, appealing the country's decision to extradite him to the United States for charges relating to the publication of military and diplomatic documents.

Cheng Lei, a prominent news anchor for the state-owned China Global Television Network, has been detained for more than 1000 days on accusations of supplying state secrets overseas.

Lei's example was one of the key points the group made, Mr Whish-Wilson said, adding that US officials were not aware of the similarity between her case and Assange.

"They weren't aware that Cheng Lei is being charged on very similar charges to Julian Assange for leaking state secrets and whenever we raise this with the Chinese government, they just laugh and go 'You hypocrites. Look what the Western nations are doing to Julian Assange'."

"We brought that up in every meeting we had and the Americans were quite surprised."

The group also emphasised to the US that Assange's source, former soldier Chelsea Manning, who had been tried, found guilty of espionage and jailed, had her 35-year sentence commuted by former president Barack Obama after seven years.

The group asked US officials why they were pursuing Assange, an Australian citizen, after rightly commuting Manning's sentence in the public interest, Mr Whish-Wilson said.

"They didn't really have an answer for that."

The contingent was made up of MPs and senators from Liberal, Labor, Greens, Nationals and independents and the unity between politicians of all stripes was one of the most powerful aspects of their campaign, Mr Whish-Wilson said.

"They hadn't seen anything like that before and we said 'we haven't done anything like this before either'."

The next steps for the cross-party group are to build up their alliance across party lines in the US, a difficult task in the face of the deep polarisation in American politics, Mr Whish-Wilson said.

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The Prime Minister will be visiting Washington on October 26 for an official state visit and Mr Whish-Wilson said he wanted Assange's extradition to be on the agenda.

With more Australian parliamentarians throwing their support behind Assange, this is going to be an issue for the US-Australia bilateral relationship, he said.

"Something I've learnt from Washington, press freedoms are not to be taken for granted," Mr Whish-Wilson said.

"They really are under pressure all around the world including in our democracies."

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