Asylum seekers on a boat that made it to within 200m of Christmas Island have not been publicly seen or heard from since residents watched a navy vessel tow the boat back out to sea last week.

Mystery surrounds the whereabouts of the boat and the welfare of its occupants as the federal government refuses to discuss it.

The boat, believed to have originated in Indonesia, was sighted close to shore by Christmas Island residents and an SBS journalist on Friday. It was then boarded by Australian officials, according to sources on the island. Photographs of the vessel were taken and circulated.

Passengers – believed to number less than 15 – were given lifejackets and the boat covered with a tarpaulin. It was then towed out to sea by a navy vessel and has not been seen since.

Australian and Indonesian advocates, lawyers and human rights organisations – who in the past have been regularly contacted by asylum seekers on board vessels trying to get to Australia – have heard nothing.

“There are simple facts that need to be established,” Greens senator Sarah Hanson-Young told Guardian Australia.

“How many people were on that boat, were there women and children on there and are they safe? The government’s obsession with secrecy should be brought to an end.”

The boat’s arrival is the first in Australian waters since 157 Sri Lankan Tamil asylum seekers were intercepted and held on board a navy vessel for a month before being sent to Nauru after negotiations with India to take them broke down.

“We can’t let another group of people go through that same trauma,” said Hanson-Young. “Hiding these boats out on the high seas, away from public scrutiny so that the Australian people don’t know what’s being done in their names simply isn’t good enough.”

Addressing the Senate on Monday, Hanson-Young asked the whereabouts of the boat and who was on it. She was also chastised for using a photograph of the boat as a prop.

“Senator Hanson-Young, if in years gone by, you had held aloft a photograph of every boat that penetrated Australian borders there would not have been enough question times in the six years of the Labor government for all the individual boats that penetrated Australia’s borders,” replied the attorney general, George Brandis.

“The Australian people know that as a result of our successful policies, the people-smuggling trade has been broken, the boats have stopped and innocent women and children are no longer in peril of being drowned at sea.”

Lawyer George Newhouse, who represented a number of the Sri Lankans held at sea last year, said there was “no transparency”.

“I can’t say whether this case is similar to the [Sri Lankan asylum seekers] because we have no idea who is on the boat and where they came from,” Newhouse told Guardian Australia.

“I’m not suggesting that the passengers might not have some right of appeal under Australian law but without a complainant and details there is little that can be done.”

On Friday the immigration minister, Peter Dutton, and the prime minister, Malcolm Turnbull, both refused to discuss the boat or its passengers, citing operational matters.

The Department of Immigration and Border Protection said on Monday its response had not changed, and referred further questions to the minister’s office. The minister’s office said the same.

On Friday Labor’s immigration spokesman, Richard Marles, labelled the response as “nothing more than a tired, lazy slogan for suppressing facts from the Australian community”.

“If these reports are true, Mr Dutton must properly and accurately detail what refugee assessment process is being undertaken in regard to any asylum seekers that have been intercepted in Australian territorial waters and provide an assurance that Australia is complying with its international obligations in respect of refugees,” he said.