SYDNEY (REUTERS) - Australia has signalled that it is preparing to ban United States whistleblower Chelsea Manning from entering the country ahead of a scheduled speaking tour, the organiser of the engagements said.

Ms Manning, the transgender US Army soldier who served seven years in military prison for leaking classified data, is scheduled to speak at the Sydney Opera House at the weekend.

However, Ms Suzi Jamil, owner of the company organising Ms Manning's speaking tour in Australia, said late on Wednesday (Aug 29) that Ms Manning had received a notice from the Australian government informing her that Canberra was considering cancelling her visa.

"We are looking for support from relevant national bodies or individuals, especially politicians, who can support Chelsea's entry into Australia," Ms Jamil said.

A spokesman for Australia's Department of Immigration declined to comment on the possible visa ban on Thursday (Aug 30).

Australian law allows the Immigration Minister to deny anyone a visa if they do not pass a character test, a broad criteria that affords the government sweeping powers.

Ms Manning is scheduled to travel to New Zealand after finishing her three events in Australia, but the centre-right opposition National Party has also called for her to be denied entry.

Ms Manning was denied entry into Canada late last year, but was subsequently allowed to appear at another event.

Ms Manning was sentenced in 2013 to 35 years in prison for sending more than 700,000 documents, videos and diplomatic cables to WikiLeaks. Her sentence was later commuted by former president Barack Obama.

The classified and sensitive documents leaked by Ms Manning - who was assigned to an army unit in Iraq as an intelligence analyst - shone a light on the nature of warfare in Iraq and Afghanistan.