The man – whose identity is known to Fairfax – was shifted to Broadmeadows around two months ago from Maribyrnong detention centre, also in Melbourne.

He had been detained since June 2009 after arriving by boat from Sri Lanka and being granted refugee protection.

But Immigration Minister Chris Bowen has been unwilling to release him since the man received a negative ASIO security assessment.

The man is among more than 50 people held in Australia's detention network found to be refugees, but not permitted to know the detailed reasons for their incarceration.

He was discovered by an Afghan detainee early this morning about 2.40am, hanging by a makeshift rope.

His attempt follows the attempted suicide of another Tamil man denied security clearance by ASIO last week.

The man, who is detained at Villawood detention centre in Sydney, had written to his case worker days earlier to say he was prepared to give his life for his brother, who is also being detained.

About 10 men are being held at the Broadmeadows centre with adverse security assessments.

Another Tamil man given an adverse security assessment is on his fourth day of hunger strike at the Broadmeadows detention centre.

Despite a High Court decision last month and a subsequent review mechanism introduced by the government for the ASIO assessments, the men in Broadmeadows have increasingly despaired at their prospects of release.

They believe Immigration authorities will soon go on leave for the Christmas break and their cases will not be examined until March or April.

A spate of suicide attempts at the Broadmeadows centre also occurred earlier this year among those affected by the ASIO assessment.

The department of immigration and citizenship has been contacted for comment.

For help or information, call Suicide Helpline Victoria on 1300 651 251 or Lifeline on 131 114, or visit beyondblue.org.au.