THE Australian Ambassador in Sudan is pleading with authorities to release from jail a Brisbane man possibly facing execution before his illness becomes fatal.

After visiting 45-year-old George Forbes in a prison in Rumbek, in southern Sudan, Ambassador Bob Bowker wrote to the president of the countryís appeals court seeking an immediate release.

A spokesman for the Department of Foreign Affairs confirmed reports out of the African nation that Forbesí health was deteriorating rapidly.

A source close to Forbes told NEWS.com.au earlier today that his health was diminishing while being inside the overcrowded prison where he and two Kenyans convicted of murdering a Ukrainian man were awaiting their sentencing.

"George looks as though he has aged at least 20 years overnight, he now has constant nausea and the cramps are coming back," the source said.

"(He feels) very, very sick and not sure he is going to make it."

The departmental spokesman said during his visit, the ambassador noticed how bad Forbesí health was.

"(Dr Bowker) gave Forbes some anti-malaria tablets and mosquito repellent," the spokesman said.

"(The) Ambassador has written to the president of the appeals court stressing our concerns for Forbesí health and welfare and seeking an urgent meeting (today) to seek his immediate release."

Disease threat

NEWS.com.au was told that overnight rain has made conditions for the 513 men at the prison even worse.

"The men (in the prison) just had to stand in the rain until it finished Ė you canít lie down because the ground becomes flooded very quickly," the source said.

"With the overflowing toilets this would be a sure way to a quick death."

As well as the possibility of Forbes contracting malaria for the expected influx of mosquitoes after the rain, the friend has said his kidney problems have flared up again.

"If something doesnít happen soon, the menís lives will be in serious danger."

Despite the only conclusive autopsy finding the victim in the case, Mykola Serebrenikov, had committed suicide, the three men were found guilty of murder on Monday.

The trio, who were working for construction company Trax International, locked the man in a room after he showed up bruised and beaten at their companyís compound on March 6.

The next morning, he was found with a sheet around his neck, hanging from a bathroom rail.

Less than 36 hours ago, Sudanese vice-president Salva Kiir assured Kenyan president Mwai Kibaki that he would look into the case before the men are sentenced