UN chief Ban Ki-moon joined Western leaders in condemning Damascus after Syrian forces killed at least 75 people during "Good Friday" protests in one of the bloodiest days of a month-long uprising.

The deaths signalled no let-up from President Bashar al-Assad, whose forces used live ammunition and tear gas against demonstrators in several towns and cities nationwide, witnesses and activists told AFP by telephone.

The bloodshed erupted as thousands of demonstrators took to the streets in order to test long sought-after freedoms one day after Assad scrapped decades of draconian emergency rule.

SANA, the official news agency, said that 10 people died in clashes between protesters and passers-by, adding that security forces intervened using only tear gas and water cannon.

Rights groups put the toll much higher,

"The Syrian security forces committed massacres in several towns and regions on Friday, so far killing 72 people and wounding hundreds," the London-based Syrian human rights committee said in a statement.

Several rights activists also published provisional lists recording the deaths of more than 70 people, with Amnesty International quoting reports saying "at least 75 people have been killed."

Friday's death toll compared with killings on March 23 in the southern town of Daraa, a focus of the protests, when activists said 100 people died.

A chorus of international condemnation rang out.

US President Barack Obama blasted Syria's "outrageous" use of violence, accusing Assad's regime of seeking Iran's aid in the brutal crackdown on the pro-democracy movement that emerged in mid-March.

"Instead of listening to their own people, President Assad is blaming outsiders while seeking Iranian assistance in repressing Syria's citizens through the same brutal tactics that have been used by his Iranian allies."

The UN chief said Assad's government must "respect international human rights, including the right to freedom of expression and peaceful assembly." and called for an independent probe into the killings."

France urged Syria to engage in a "political dialogue without delay", while European Parliament chief Jerzy Buzek called for the release of all prisoners of conscience and British foreign secretary William Hague said the killing of demonstrators is "unacceptable."

Amnesty, citing Syrian activists, said: "At least 75 people have been killed on Friday in Syria during mass protests. As the government launched its deadliest crackdown yet on demonstrators calling for political reform."

According to Amnesty, 30 people were killed in the southern town of Ezreh, 22 in Damascus, 18 in the central city of Homs and the rest in other parts of the country.

Two boys aged seven and 10 were among those killed in Izrah.

"The Syrian authorities have again responded to peaceful calls for change with bullets and batons," said Amnesty's West Asia and North Africa director Malcolm Smart."

Thousands of protesters chanting "freedom, freedom," and calling for the fall of the regime swarmed cities across Syria on Friday from Qamishli in the Northeast to Daraa, the protest hub, in the South, witnesses said.

There were protests also in the capital Damascus and the Northern suburb of Douma, they told AFP.

Assad, in power since replacing his father Hafez as President in 2000, issued decrees on Thursday scrapping emergency rule, abolishing the state security court and allowing citizens to hold peaceful demonstrations.

But his detractors said the moves were not enough, and the so-called Syrian local coordinating committees of protesters made a raft of demands, urging a halt to the torture, killings and arrests of protesters.

Friday's protests came after a call by Facebook group The Syrian revolution 2011 for rallies spanning the Christian and Muslim faiths on "Good Friday," which commemorates Jesus Christ's crucifixion.

Friday is also the Muslim day of rest when the biggest demonstrations have been staged across Syria after weekly prayers.

Before on Friday, security forces and plain-clothes police had killed about 220 people in a brutal crackdown on the protests, according to Amnesty International.