Syrian troops fired on mourners at a funeral and raided an eastern city, killing at least 50 people in an intensifying government crackdown on protesters.
More than 300 people have died in the past week, the bloodiest in the five-month uprising against President Bashar Assad.
Syria's Arab neighbors forcefully joined the growing international chorus of condemnation against Assad's regime for the first time on Sunday.
The king of Saudi Arabia, whose country does not tolerate dissent and lent its military troops to repress anti-government protests in neighboring Bahrain, harshly criticized the Syrian government and said he was recalling his ambassador in Damascus for consultations.
"What is happening in Syria is not acceptable for Saudi Arabia," King Abdullah said in a written statement on Monday.
"Syria should think wisely before it's too late and issue and enact reforms that are not merely promises but actual reforms," he said. "Either it chooses wisdom on its own or it will be pulled down into the depths of turmoil and loss."
The Saudi king's statement came the day after the Gulf Cooperation Council urged Syria to "end the bloodshed" as the international pressure mounts.
The 22-member Arab League, which had been silent since the uprising began, said Sunday it is "alarmed" by the situation in Syria and called for the immediate halt of all violence.
The US envoy to Damascus, Robert Ford, who returned to Syria on Thursday, also said in a US television interview on Sunday that Washington will "try to ratchet up the pressure" on President Bashar al-Assad's regime.
Earlier in the day, Syrian forces have launched an assault on two towns, reportedly killing dozens of people in an increasingly violent crackdown on anti-government protests.
According the Local Co-ordination Committees of Syria, an opposition human rights group, government forces killed more than 70 people across several cities.
Activists also told Al Jazeera on Sunday that troops had killed at least 50 people in the eastern city of Deir ez-Zor alone.
The city was under siege and electricity and phone lines were cut, according to another source.
"Shelling has been heard in several areas," Rami Abdel Rahman, head of the UK-based Syrian Observatory for Human rights, told the AFP news agency.
He also said that a sweeping campaign of arrests followed with "dozens" of people being taken into custody.
Seven people, including two children, were also reported killed in the town of Al Holeh in the central Homs province.
Abdel Rahman said about 25 tanks and troop carriers had entered Hula and carried out military operations.
Arab League condemnation
Sunday's deaths come as international condemnation of the violence against protesters - most recently from the Arab League - continued to mount.
The Arab League, through its secretary-general Nabil El Araby, expressed "growing concern" over the "deteriorating" situation in Syria.
In a statement on Sunday, El Araby specifically mentioned Hama and Deir ez-Zor, but also referred to violence against protesters in all of Syria.
He also called for a comprehensive national dialogue, saying the Arab League is prepared to provide any necessary assistance to this end, and that such a dialogue is "the only solution that would guarantee a peaceful transition to stability".
In a veiled reference to a possible NATO intervention, the statement concluded with a reminder that the Arab League charter rejects foreign intervention in Arab countries' affairs.
Meanwhile, President Bashar al-Assad defended his security forces' deadly crackdown on anti-regime protests as the "duty of the state" to confront "outlaws."
"Syria is on the path to reforms," he said, quoted by state news agency SANA. "To deal with outlaws who cut off roads, seal towns and terrorise residents is a duty of the state which must defend security and protect the lives of civilians".
His statement came a day after Turkish Prime Minister Tayyip Erdogan gave a stark warning to Assad on Saturday that his country's patience is running out with Syrian regime over its bloody crackdown on protesters.
"Our patience s running out. Therefore I am sending Turkish foreign minister to Syria to hold all the necessary talks there," Erdogan said.
In-depth coverage of escalating violence across Syria
"Our messages will be conveyed to them clearly during this visit and the upcoming process will be shaped according to their response and steps that will be taken."
He said the minister would go to Syria on Tuesday.
Responding to the announcement, Assad's adviser, Bouthina Shaaban, said Turkey could expect an "even firmer" reply.
"If the Turkish Foreign Minister Ahmet Davutoglu is to deliver a firm message to Syria, he will hear more decisive reply regarding the Turkish stance which didn’t condemn the brutal killing and crimes committed by the armed terrorist groups against the civilians, military and police members till now," SANA quoted her as saying.
'Excessive use of force'
Pope Benedict XVI also spoke out against the violence, asking for the "legitimate aspirations" of the Syrian people to be met and for a return to peaceful coexistence.
"I am following with deep concern the dramatic and increasing episodes of violence in Syria that have led to numerous victims and grave suffering," the pontiff said in a weekly address to pilgrims.
UN Secretary-General Ban Ki-moon on Saturday called on Assad to halt the use of force against civilians "immediately".
Ban spoke to the president by phone to express "his strong concern and that of the international community at the mounting violence and death toll" in the country over the past week, the UN press office said in a statement.
The Assad government has sought to crush the country's protest movement with force, killing around 1,650 civilians and arresting thousands of dissenters since March, according to the Syrian Observatory for Human Rights.
In an apparent attempt to calm the unrest, Walid al-Muallem, Syria's foreign minister, on Saturday promised "free and fair" general elections by the end of the year. He said the new parliament will represent the aspirations of the Syrian people.
The four-year term of the current parliament expired earlier this year and Assad is expected to set a date for new legislative elections before the end of 2011.