More than 60 Australian federal politicians have explicitly called on the US to drop the prosecution of Julian Assange, warning of “a sharp and sustained outcry in Australia” if the WikiLeaks founder is extradited. With a small cross-party delegation due to fly to Washington next week, the Guardian can reveal the lobbying trip has won the open support of 63 members of Australia’s House of Representatives and Senate. In a letter, the 63 MPs and senators said they stood in support of the trip to the US and were “resolutely of the view that the prosecution and incarceration of the Australian citizen Julian Assange must end”. They said the matter had “dragged on for over a decade” and it was “wrong for Mr Assange to be further persecuted and denied his liberty when one considers the duration and circumstances of the detention he has already suffered. “It serves no purpose, it is unjust, and we say clearly – as friends should always be honest with friends – that the prolonged pursuit of Mr Assange wears away at the substantial foundation of regard and respect that Australians have for the justice system of the United States of America,” the letter said. Sign up for Guardian Australia’s free morning and afternoon email newsletters for your daily news roundup Assange remains in Belmarsh prison in London as he fights a US attempt to extradite him to face charges – including under the Espionage Act. The charges are in connection with the publication of hundreds of thousands of leaked documents about the Afghanistan and Iraq wars, as well as diplomatic cables, in 2010 and 2011. Assange sought refuge in the Ecuadorian embassy in London in 2012 and remained there until 2019. The Australian citizen was arrested when Ecuador revoked his diplomatic status and has been in jail since then, amid a series of legal challenges against the US extradition bid. The Australian MPs and senators said they agreed with comments by the prime minister, Anthony Albanese, that “enough is enough … and that nothing is served from the ongoing incarceration of Julian Assange”. They also welcomed the recent backing of the opposition leader, Peter Dutton, saying this bipartisan position was “matched by the wide cross-party and independent support within the Australian parliament itself, which in turn reflects the strongly held views of the Australian community”. “Let there be no doubt that if Julian Assange is removed from the United Kingdom to the United States there will a sharp and sustained outcry in Australia.” The letter was organised by the co-conveners of the Bring Julian Assange Home Parliamentary Group: the independent MP Andrew Wilkie, the Labor MP Josh Wilson, the Liberal MP Bridget Archer and the Greens senator David Shoebridge. The total number of signatories – 63 Australian federal politicians – reflects an increasing cross-party consensus on the issue. It compares with 48 who signed a letter to the US attorney general, Merrick Garland, in April. New backers of the cause include Shayne Neumann and Louise Pratt of the governing Labor party, and Melissa Price of the opposition Coalition. The Australian politicians noted “with gratitude the considerable support in the United States for an end to the legal pursuit of Mr Assange from members of Congress, human rights advocates, academics, and civil society, and from within the US media in defence of free speech and independent journalism”. “On that basis we ask Congresspeople, members of the press, and other relevant civil society stakeholders in the United States to speak up now in supporting an end to the prosecution and detention of Julian Assange,” they wrote. The Australian politicians said they believed the “right and best course of action” would be for the US Department of Justice to cease the prosecution. Alternatively, they said, “a decision to simply abandon the extradition proceedings would have the sensible, just, and compassionate effect of allowing Mr Assange to go free from a prolonged and harsh period of high-security detention”. The US secretary of state, Antony Blinken, has previously pushed back at the Australian government’s complaints that the pursuit of Assange had dragged on too long. During a visit to Australia in July, Blinken said he understood “the concerns and views of Australians”. But he added that it was “very important that our friends here” in Australia understood the US concerns about Assange’s “alleged role in one of the largest compromises of classified information in the history of our country”. Blinken said Assange was alleged to have “risked very serious harm to our national security”. The White House has previously said Joe Biden is committed to an independent Department of Justice. Albanese is due to meet the president during an official visit to the US, including a state dinner, on 25 October. Assange’s brother, Gabriel Shipton, said: “Australians are told that we are great mates with our American friends, but Julian’s treatment says otherwise. It’s up to the prime minister to take this message and use the support from within the electorate to free Julian.”