Story highlights The opposition reports 78 killed, most in Idlib

Monday's toll may be worst of the uprising to date

The threat to execute terrorists is a major escalation against protesters

The United Nations estimates that about 5,000 have died in Syrian violence this year

Dozens more people were reported killed by government troops and police in Syria on Tuesday, a day after what opposition activists said was the single deadliest known day of anti-government protests.

The Local Coordination Committees, an opposition umbrella group, said 78 people died across four Syrian provinces. Most of them were in Idlib, where the London-based Syrian Observatory for Human Rights reported that 60 to 70 Syrian army defectors were gunned down Monday as they tried to flee their posts.

The Syrian Observatory's Rami Abdul Rahman said another 40 civilians were killed the same day "across Syria during house-to-house raids, arrests, and clashes between army defectors and the Syrian army."

"Monday may have been a day with the highest death toll in Syria, between 100 and 110 killed in total," he said.

The Syrian government maintains that it is cracking down on armed terrorists who attack security forces and civilians. The activists say the government's brutal crackdown against peaceful protests has led to the deaths.

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CNN could not independently verify the allegations because Syria restricts the activity of journalists in the country, and the Syrian government did not immediately respond to the claim.

Tuesday, the LCC said 59 people were killed in Idlib, with another 14 in Homs, three in Hama and two in Daraa. All had been shot to death by government forces, the group said.

The uprising against the Bashar al-Assad regime has claimed an estimated 5,000 lives since March, the United Nations says. As violence raged on Tuesday, state television announced that the government will execute anyone who participates in terrorist acts or distributes weapons.

A new law published Tuesday specifies that anyone who distributes weapons for the purpose of committing terrorist acts will get the death penalty, according to the state-run Syrian Arab News Agency. It also mandates a life sentence of hard labor for weapons smugglers who intend to traffic them for terrorist acts.

Monday's deaths came the same day that Syria signed an Arab League proposal aimed at ending the violence. The Arab League expelled Syria over its crackdown.

The signing came just days after the Cairo-based group of Arab nations warned it could ask the U.N. Security Council to intervene in the restive country.

Syrian Foreign Minister Walid Moallem announced Monday that Damascus had signed the deal, insisting: "We want a political solution. I do not want the killings to go on."

On Tuesday, permanent members of the Arab League met in Cairo, saying they welcomed the signing of the proposal. Members also stressed "the emphasis and the paramount importance of the commitment of the Syrian government to fully implement" the accord.

Syrian opposition leader Burhan Ghalioun was not impressed by the signing of the agreement.

"The Syrian regime is playing games and wants to buy time. We are quite surprised that the Arab League is allowing this to take place," the head of the Syrian National Council said Monday in comments on Orient TV from Tunisia.

Separately, Ghalioun urged the international community to enforce a buffer zone to protect civilians.

Council members meeting in Tunisia declined to say whether they would support the use of foreign military force to enforce such a zone, but stressed their belief that international intervention is necessary.

"This regime has proven time and time again that it is a regime built on lies and force," Ghalioun told CNN. "We need a safety zone to protect and prevent efforts by the regime to transform the crisis into a civil conflict."

Five Arab League ministers drafted a resolution Saturday calling for the end of violence and approving an observer mission in Syria.

World powers have denounced the Syrian government's activity, saying they are looking for ways to rein in violence and urgently contain the threat of civil war that is reflected in the emergence of the armed defector force.