Ammash says the whole family is worried about the health of her sister, who was arrested on 5 May 2003 for her alleged role in Iraq's biological weapons programme.
"I am sad, angry and anxious because we have not been able to verify the information that suggests she is dying in custody," Ammash said.
"I have been trying to contact the Red Cross and the US authorities here in Iraq but to no avail.
"The last time we spoke to her was three weeks ago, when she was allowed to call us at home. In the last two weeks we were told twice to wait for her call but she never rang."
Nada Ammash said: "Last week we received a phone call from the US military telling us to gather at the family home the next day because Dr Huda would call. We did get together but the telephone never rang."
Top scientists and academics in
Iraq have been assassinated
Huda Ammash has met her family twice since she was jailed. The first meeting was in November 2003 when her mother was allowed to visit her, but it was not until September 2004 that she was able to meet the whole family.
Ammash said her sister has been suffering from cancer for years, and has been under regular medical observation while in custody.
But the US military insists it is providing adequate medical care for its former government detainees and that Ammash is in good health.
"We are aware that she had been treated for cancer at one time, prior to ever being detained. She is checked routinely to ensure there is no reoccurrence. We have no immediate concerns for her health," a US military officer said.
Nada Ammash said she plans to sue media outlets that have promoted her sister as "Mrs Anthrax" once Huda Ammash's ordeal comes to an end.
"My sister is a scientist with a human interest. She devoted herself to save the victims of depleted uranium and carried out extensive research in that field," she said.
"I will take legal action against those who have promoted her as a killer and tarnished her reputation in the eyes of people in Iraq and around the world," she said.
"I will take legal action against those who have promoted her as a killer and tarnished her reputation in the eyes of people in Iraq and around the world"
sister of Huda Ammash
Huda Ammash was born in Baghdad in 1953 and earned her degree in biology/microbiology from Baghdad University in 1975. She pursued her higher studies at Texas University in the US, where she got her masters degree in microbiology. In 1983, she got her PhD from the University of Missouri.
In Iraq, she was a professor at Baghdad University and held a senior position at the regional command of the Baath Party. She was the first and only woman member of the regional command of the party.
Her father was a well-known Iraqi statesman and army officer. He became a defence minister in 1963, vice-prime minister in 1968 and an ambassador in 1970.
In Beirut, Lebanon, the Arab Forum appealed in a statement received by Aljazeera.net for immediate action to "protect jailed Iraqi scientists".
The statement said the forum has sent letters to the heads of the UN and Arab League as well as other organisations urging them to take action to protect Iraqi scientists currently in US custody in Iraq.
The statement blamed the assassination of 125 Iraqi scientists and professors since the US invasion of Iraq in April 2003 on Israel's Mossad intelligence service and held the US military responsible for the safety of Iraqi scientists in its custody.