Amnesty International has received first-hand reports of torture and other ill-treatment from detainees held in Syria as a wave of arrests of anti-government protesters intensified over the weekend.

Detainees who were recently released told the organization of beatings and harsh conditions in detention, raising fears for the safety of hundreds of others being held, including at least 499 people who were arrested on Sunday in house-to-house raids in the southern town of Dera’a.

“These disturbing new accounts of detainees being tortured further underscore the need for President Bashar al-Assad to put an end to his security forces’ violent onslaught against his own people,” said Philip Luther, Amnesty International’s Deputy Director for the Middle East and North Africa.

“The use of unwarranted lethal force, arbitrary detention and torture appear to be the desperate actions of a government that is intolerant of dissent and must be halted immediately. Syrians must be allowed to voice their calls for change peacefully.”

The army announced on Sunday it had arrested 499 just in Dera’a, which has been a key location for pro-reform protests that have swept the country.

Widespread arbitrary arrests have also taken place in recent days in other towns and cities around the country, including Qamishly in the north-east, az Zabadani and Madaya (west of Damascus), Duma (near Damascus) and the coastal town of Latakia.

Among the many arrested are political and social activists, including ‘Omar Qashash, an 85-year-old former political prisoner, 77-year-old lawyer Hassan ‘Abdel ‘Azim of the Democratic Arab Socialist Party, and ‘Abd al-Rahman Hamada, a 20-year-old student taken from his home on 30 April by security forces who were searching for his brother Wa’el. Wa’el Hamada and his wife Razan Zaitouneh, a human rights activist and leading human rights lawyer, respectively, have gone into hiding.

Most are held at unknown locations without any access to visits from their families or lawyers, adding to fears for their safety.

Two men who were detained last month in the coastal city of Banias told Amnesty International that Syrian security forces had used rifle butts to hit them and many other detainees on the neck and collarbone.

One detainee said that after being stripped and beaten he was made to lick his blood off the floor. According to him, he and others detained with him had been beaten with sticks and cables as well as kicked and punched. Held without food for three days in overcrowded conditions in one detention centre, he said they had to resort to drinking dirty water from a toilet.

Amnesty International has obtained the names of 54 people killed on Friday, bringing to 542 its figure for the total number of protesters, bystanders and others who have been killed during six weeks of pro-reform protests. The actual number of deaths is almost certainly higher.

The high number of deaths has been attributed to heavy-handed tactics by Syrian security forces, who have shot live bullets directly into protests and funeral processions and used tanks to shell residential buildings. The military last week laid siege to Dera’a, cutting off electricity and water supplies.

On 29 April the UN Human Rights Council condemned the ongoing grave human rights violations in Syria and called for a UN fact-finding mission to investigate.

President Bashar al-Assad’s government has accused “armed terrorist groups” of leading a violent uprising and of being responsible for the deaths of nearly 80 members of the security forces.

Amnesty International has not been allowed to visit Syria since the protests began. The international media has also been severely restricted; foreign journalists have generally not been allowed into the country. Al-Jazeera confirmed to Amnesty International today that its journalist Dorothy Parvaz has not been seen since arriving at Damascus airport from Qatar on 29 April.

“We fear that many of the hundreds currently detained by the Syrian authorities have been arrested arbitrarily,” said Philip Luther.

“Those detained merely for their involvement in peaceful protests are prisoners of conscience and should be released immediately and unconditionally. Those suspected of committing an internationally recognizable criminal offence should be charged without delay and brought to justice in fair trial proceedings.”