The Palestinian captors of Israeli soldier Gilad Shalit have broadcast what they say is his first audio message since his capture a year ago.
The voice on the tape says his health is worsening and he needs medical help.
The recording was put on a website of the military wing of Hamas. Cpl Shalit was seized near the Gaza border in a joint raid by three militant groups.
Hamas has demanded the release of prisoners from Israeli jails, but Israel ruled out any negotiations.
Foreign Minister Tzipi Livni said Hamas was making "cynical use of the suffering of Gilad Shalit".
She was speaking as leaders from Israel, Egypt and Jordan met in the Egyptian resort of Sharm el-Sheikh, in an apparent show of support for Palestinian Authority President Mahmoud Abbas.
Mr Abbas is engaged in a bitter power struggle with Hamas militants, who have taken over the Gaza Strip.
In the message, posted on a website supporting the Ezzedine al-Qassam Brigades, the man purported to be Cpl Shalit is heard speaking Hebrew.
"I've been in prison one year. My situation is deteriorating. I need an extended period in hospital," the voice says.
"I am sorry that the Israeli government has not shown more interest. It should meet the demands of my kidnappers so I can be released."
It was not possible to authenticate the tape, although Cpl Shalit's father, Noam, told Israeli media it sounded genuine.
Israeli officials said they had no doubt that the text had been dictated by Hamas to the 20-year-old soldier.
Earlier, a spokesman for the militants holding him said he was in good health.
Abu Mujahid, of the Popular Resistance Committees, said Cpl Shalit was being treated according to Islamic law.
Shalit's family have attended a rally marking one year of captivity
The Hamas militants have also released what purports to be video footage of the raid in which Cpl Shalit was captured on 25 June 2006.
The operation was claimed by the al-Qassam Brigades, the Popular Resistance Committees, and the Army of Islam, and triggered a large-scale Israeli operation in the Gaza Strip.
Cpl Shalit's captors have handed over a list of prisoners they want freed in exchange for him.
About 10,000 Palestinian prisoners are being held in Israeli jails, some without charge.
Egypt has been trying to broker the soldier's release, but the negotiations have been suspended because of the unrest in the Palestinian territories.
On Sunday, Noam Shalit criticised Israeli Prime Minister Ehud Olmert for not doing more to secure his son's release.
"It's the test of a leader," said Mr Shalit. "If you do not know what to do, give your portfolio to someone who can bring about results immediately."
Israeli human rights group B'Tselem has accused Cpl Shalit's captors of committing a war crime.
"International humanitarian law absolutely prohibits taking and holding a person by force in order to compel the enemy to meet certain demands, while threatening to harm or kill the person if the demands are not met," the group said.
"Furthermore, hostage-taking is considered a war crime."
Abu Mujahid brushed off B'Tselem's accusation, saying the soldier was a prisoner of war who had been captured inside a tank used to fight Palestinians.
"Any occupiers on the land are a legitimate target because they are soldiers," he said.