BEIRUT (AP) -- Machine-gun fire and explosions erupted inside a Syrian city at the heart of the country's uprising Wednesday as activists reported two grisly attacks that killed at least 20 people in the past 24 hours.

The fresh bloodshed suggests Syria is sliding toward chaos nearly eight months into the uprising against President Bashar Assad. The Arab League was expected to unveil a plan Wednesday to ease the violence, calling for withdrawal of tanks and armored vehicles from the streets and free elections, diplomats involved in the process said.

The violence shook residents of Homs, which has endured the brunt of the Syrian government's brutal crackdown on dissent since the revolt began in mid-March. It was not clear who was behind the latest attacks, and there were increasing signs that the crisis was exacerbating religious and sectarian tensions.

The Syrian opposition's two main activist groups said gunmen attacked factory workers in the village of Houla on Wednesday, killing 11 people. Majd Amer, an activist in Homs, said some of the men were decapitated and others shot in the head, their hands tied behind their backs.

Amateur videos posted online showed the men, bound and gagged, lying on the ground.

The killing spree amounted to a "massacre," said the activist groups, the British-based Syrian Observatory for Human Rights and the Local Coordination Committees activist network.

The wave of violence apparently started late Tuesday.

Amer and activist Mohammad Saleh in Homs said gunmen attacked a bus carrying workers returning from their jobs, killing nine passengers. They said the gunmen stopped the bus, released the women passengers, and then killed the others.

The activists said the army brought in heavy reinforcements to the streets of Homs on Wednesday morning. Heavy machine-gun fire and explosions could be heard on the streets and residents said most people had stayed home because of the violence.

Syria has largely sealed off the country from foreign journalists and prevented independent reporting, making it difficult to confirm events on the ground. Key sources of information are amateur videos posted online, witness accounts and details gathered by activist groups.

On Wednesday the Arab League was set to unveil its proposal on the Syrian crisis during a meeting at the group's headquarters in Cairo.

Details have not officially been released, but it appears to be the most wide-reaching effort yet to address the uprising and comes with a sharp rebuke to Assad's regime for its bloody crackdowns on anti-government protesters.

The U.N. says some 3,000 people have been killed since the revolt began in March.

Syria's state-run media said late Tuesday that Damascus has agreed to an Arab League plan, but a senior Arab League official said the body had not yet received a response from Syria.

Arab diplomats involved in the process told The Associated Press the proposal also calls for release of all political prisoners, a new constitution and free presidential and parliamentary elections that should be monitored by foreign observers. The diplomats spoke on condition of anonymity because the proposal is not yet public.

The plan also provides for a dialogue between the Syrian government and opposition representatives in Cairo. However, the opposition has refused to enter into any dialogue as long as Assad remains in power.

The proposal is the latest in a string of international efforts to ease the crisis, which has led to international condemnation of the Syrian regime. European Union and U.S. sanctions are chipping away at Syria's ailing economy, and many world leaders have called on Assad to step down.

The diplomats said Arab League countries disagreed over parts of the proposal. Gulf Arab nations were pushing to suspend Syria's league membership if it does not accept, while others like Egypt and Sudan were arguing for continued engagement with the regime.

All agreed on the importance of not letting Syria become another Libya, where eight months of brutal civil war preceded the capture and killing of Moammar Gadhafi last month.

Throughout the crisis, Syria's regime has remained defiant. In recent days, it has mined its border with Lebanon, apparently to prevent opposition figures from fleeing, and Assad has vowed that the Middle East will burn if foreign powers intervene.

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Hubbard reported from Cairo.

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