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 urges Arab League delegates meeting on Saturday to suspend Syria from their organisation, asks the United Nations to impose sanctions on individuals responsible and refers 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 2 November when the Syrian government agreed to 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 neighbouring 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 armoured vehicles, to fire into neighbourhoods to frighten people before entering with armoured personnel carriers and other military vehicles," Human Rights Watch said.

"They cut off communications and established checkpoints restricting movement in and out of neighbourhoods 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 "defence 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".

Arab states remain widely divided over how to deal with Syria's crackdown on protesters after a peace plan brokered by its neighbours failed to stem violence, and there is little likelihood a meeting on Saturday will bridge the gap.

In preparation for the meeting set to take place on Saturday, protesters camped out in front of the Arab League headquarters have expressed their anger to the Arab League’s stance on Syria.

On Friday, several activists announced plans to hold a symbolic funerary procession for the Arab League in response to its weak stance towards the regime. They have also echoed the need for the Arab League to freeze Syria’s membership and to open up the possibility of recognising the Syrian National Council (SNC) as the country’s legitimate representative.     

On Wednesday, several protesters blocked a high-profile group of veteran Syrian dissidents, including writer Michel Kilo and militant Haytham Manaa, from entering Arab League headquarters, hurling eggs at them.

The visitors to the League's offices in Cairo were to meet the league's chief ahead of a meeting on Syria due to be held on Saturday. Protesters expressed their anger at the group of dissidents as traitors. Additionally, they condemned them for not backing the SNC’s demands for Syria's exclusion from the pan-Arab body and for imposing a no-fly zone over the country.