"The use of lethal force against peaceful demonstrators and their arbitrary arrests are unacceptable," said Ban, according his spokesman Martin Nesirky.
Ban "urges the Syrian authorities to refrain from violence and to abide by their international commitments regarding human rights which guarantee the freedom of opinion and expression, including the freedom of the press and the right to peaceful assembly."
Ban "believes that, as elsewhere, it is the responsibility of the government in Syria to listen to the legitimate aspirations of the people and address them through inclusive political dialogue and genuine reforms, not repression," Nesirky said.
The statement came as the United States said it "strongly condemns the violence that has taken place in Syria," and called on the Syrian government "to allow demonstrations to take place peacefully," said National Security Council spokesman Tommy Vietor.
Security forces fired live bullets at protesters, killing at least four people, said a human rights activist in Daraa contacted by AFP from Nicosia.
"Hundreds of protesters were wounded and many were snatched by the security force from the hospital where they had been taken and removed to an unknown location," the activist added.
Similar demonstrations were reported in the coastal town of Banias, in Homs, north of the capital, as well as in Damascus,
Plain-clothes police broke up a protest after Friday prayers at the main mosque in central Damascus and dragged away at least two activists, AFP reporters witnessed.
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