Homs has emerged as a centre of protest against President Bashar al-Assad.
Human Rights Watch has called on the Arab League to suspend Syria, saying the abuses against civilians in Homs are crimes against humanity.
The city has been a focus for anti-government demonstrations. Dozens were reported killed there on Thursday.
The UN says at least 3,500 people have been killed in Syria in protests against President Bashar al-Assad.
The government blames the unrest on armed gangs and militants and say hundreds of soldiers and police have been killed.
But Sarah Leah Whitson, Middle East director at Human Rights Watch said the city of Homs represented: "A microcosm of the Syrian government's brutality".
She said that the Arab League, who are due to meet to discuss the crisis in Syria, must apply pressure after the country failed to honour the League's plan to end the unrest.
"The Arab League needs to tell President Assad that violating their agreement has consequences, and that it now supports Security Council action to end the carnage."
'Detainees tortured'
Syrian authorities had agreed in early November to withdraw from restive cities, set political prisoners free and start talks with the opposition.
But, since then, the UN says that the killing has continued.On Thursday, nearly 40 people were killed across the country, including five soldiers and an eight-year-old girl, Syrian activists said.
The eight-month-old uprising has become increasingly armed, with Syrian soldiers joining the anti-government protesters in some areas, including Homs.
The city has seen repeated clashes between army defectors and security forces, who have been mounting raids in pursuit of protesters.
Human Rights Watch said it had conducted more than 110 interviews with witnesses and victims of the violence in Homs, both the city and the surrounding province of the same name.
In a report, entitled We Live As In War, HRW documents what it says are "dozens of incidents in which security forces and government-supported militias violently attacked and dispersed overwhelmingly peaceful protests".
The HRW witnesses describe security forces firing machine guns or heavier weapons into districts of cities where protests have been taking place, to frighten the residents.
The CA's Jonathan Head, in neighbouring Turkey, says the report backs up accusations against the Syrian authorities by activists.
However, the allegations cannot be independently verified because the Syrian government has banned most foreign journalists from entering the country.
'Shot in stomach'
Checkpoints around the district are set up to control movement and troops in armoured vehicles move in to conduct raids.One resident of Homs told HRW that when he and others tried to bring food into Bab Sba' district, security forces opened fire, killing one person and wounding another in his group.
One woman protesting in Homs on 15 August with her family told HRW: "It was calm, so everything seemed OK.
"Then two cars showed up suddenly and opened fire, targeting people even as they were ducking and lying on the ground. They were white Kia Cerato cars with tinted windows, like those used by air force intelligence," she said.
Her son was shot in the stomach. "The doctors were able to remove the bullet, but it left a lot of damage," she said.
Thousands of people have been arrested since the anti-government protests began in March. While most are eventually released, HRW says several hundred are missing.
Former detainees interviewed by HRW described being tortured with heated metal rods, electric shocks, beatings and being forced into "stress positions" for long periods.
"They beat [me] with cables and then hanged me by my hands from a pipe under the ceiling so that my feet weren't touching the floor," one former detainee said.
"They were beating me, and pouring water on me, and then using electric stun guns," he added.
HRW said it had independently confirm 17 deaths in custody. Twelve of these people "bore unmistakable marks consistent with torture, including bruises, cuts and burns".
