The United States has strongly condemned what it calls Syria's outrageous use of violence against anti-government protesters as activitists reported at least 32 people killed in fresh clashes on Friday.
In a statement, the White House said the Syrian government was leading the country down a "dangerous path" and called for "an immediate end to the brutality and violence".
The United Nations Secretary General Ban Ki-moon has described the use of military force as "unacceptable".
A spokesperson for Mr Ban says he is "keen to speak to" Syria's president but that Bashar al-Assad has repeatedly been "unavailable" in recent days.
Syria has prevented foreign journalists from entering the country, making it difficult to independently verify reports from there, but opposition groups say security forces opened fire on crowds in several areas, including the capital, Damascus.
They accused the Syrian army of a scorched-earth policy around Jisr al-Shughur, saying helicopter gunships and tanks have been firing into the town while advancing troops have bulldozed homes and set fire to crops and fields.
The BBC reports that the government blamed "armed groups" for the deaths of 120 security personnel in Jisr al-Shughour earlier this week, but some reports said the troops were shot after a mutiny.
The government says local residents requested the army's intervention to restore peace and quiet.
Activists say tanks and helicopters also opened fire in the northern town of Maarat al-Numan, leaving at least 10 protesters dead and many others wounded.
Correspondents say it is the first reported use of air power to quell protests in Syria's three-month uprising.
Human rights groups say more than 1300 people - most of them unarmed civilians - have died as the government led by President Bashar al-Assad tries to suppress dissent.
Since March, mass protests against the Assad regime have become a regular event following Friday prayers.
The regime has prevented foreign journalists from entering the country, making it difficult to verify reports from there.
Refugees flee into Turkey
Meanwhile, a new camp is being constructed in Turkey to house the growing number of refugees fleeing the fighting in Syria.
Turkish officials instructed the Red Crescent humanitarian organisation to set up a new camp capable of housing 5000 people.
According to the BBC, minibus drivers who have been employed to take the refugees from the border say they have moved more than 1500 people in the past couple of days.
Turkish prime minister Recep Tayyip Erdogan has previously been reluctant to criticise Syria, but in an interview quoted by the Anatolia news agency he said the Assad regime was committing atrocities against anti-government demonstrators.