BEIRUT (Reuters) - Syrian government forces have carried out crimes against humanity as they try to crush opposition to President Bashar al-Assad in the restive province of Homs , Human Rights Watch said in a report released on Friday. It urged Arab League delegates meeting on Saturday to suspend Syria from their organization, ask the United Nations to impose sanctions on individuals responsible, and refer Syria to the International Criminal Court. "The systematic nature of abuses against civilians in Homs by Syrian government forces, including torture and unlawful killings, constitute crimes against humanity," the group said in a statement accompanying the report. HRW said Syrian security forces had killed at least 104 people in Homs since November 2, when the Syrian government agreed an Arab League plan aimed at ending the violence and starting a dialogue with Assad's opponents. Those deaths followed the killings of at least 587 civilians in Homs between April and August, the group said, the highest death toll of any single governorate in the country. "Homs is a microcosm of the Syrian government's brutality," said Sarah Leah Whitson, Middle East director at Human Rights Watch. "The Arab League needs to tell President Assad that violating their agreement has consequences, and that it now supports (UN) Security Council action to end the carnage." The United Nations says 3,500 people have been killed in Assad's crackdown on protests which erupted in mid-March, inspired by popular Arab uprisings which have toppled three North African leaders. Authorities blame armed groups for the violence, saying they have killed 1,100 soldiers and police. Syria has barred most foreign media, making it difficult to verify accounts of opposition activists or officials. Human Rights Watch said it was also refused access to Syria and described the task of obtaining accurate information as "challenging." Its report was based on interviews with 114 Homs residents, who had either fled to neighboring countries or who spoke via the Internet from inside Syria. It said security forces had conducted large-scale military operations in several towns in the province, including Homs city and the town of Tel Kelakh on the border with Lebanon. "Typically, security forces used heavy machine guns, including anti-aircraft guns mounted on armored vehicles, to fire into neighborhoods to frighten people before entering with armored personnel carriers and other military vehicles," Human Rights Watch said. "They cut off communications and established checkpoints restricting movement in and out of neighborhoods and the delivery of food and medicine." Thousands of people in Homs -- as in the rest of the country -- were subjected to arbitrary arrest, enforced disappearances and systematic torture in detention, the group said. Most were released after several weeks in detention, but several hundred were still missing. HRW said it had documented 17 deaths in custody in Homs , at least 12 of which were clearly from torture. "Torture of detainees is rampant," it said, adding it had spoken to 25 former detainees in Homs , all of whom reported being subjected to various forms of torture. It quoted one man, held at the Military Intelligence base in Homs , as saying he was beaten with cables and hanged by the hands from a pipe so that his feet did not touch the ground. "I was hanging there for about six hours, although it was hard to tell the time. They were beating me, and pouring water on me, and then using electric stun guns," he said. Human Rights Watch said army defections had increased since June and that some residents in Homs had formed "defense committees" armed with guns and even rocket-propelled grenades. Syria's state media and activists have reported several assassinations in the city over recent weeks of people seen as sympathetic to Assad. "Violence by protesters or defectors deserves further investigation," Human Rights Watch said. "However, these incidents by no means justify the disproportionate and systematic use of lethal force against protesters."