Violence swept across Syria on Friday, with at least 43 people reported killed in another bloody day of confrontation between government forces and demonstrators calling for political change.

Reliable numbers were difficult to come by. CNN bases its figures on reports from witnesses. Amnesty International, citing local human rights activists, reported that at least 75 people were killed in Friday's protests. The Syrian government does not permit CNN to report from inside the country.

The killings occurred in several flashpoint regions as thousands of Syrian protesters defiantly marched after Muslims' weekly prayers in a display of mass discontent toward the government.

Violence ripped through the Damascus suburbs of Douma, Moademy and Zamalka, and other cities -- Homs, Harasta and Izraa. The state-run news agency reported demonstrations and clashes, citing injuries but no deaths.

Human rights groups and witnesses told a different story. "Today, they have killed so many people. There are so many people injured and people have been kidnapped," Wissam Tarif, a human rights activist, told CNN. "They are acting as an armed gang, not as security forces."

In the city of Homs, near Syria's western border with Lebanon, one man said a fellow demonstrator was shot in the head, put into a car by other demonstrators and driven off as others in the crowd fell to sniper fire.

"They were shooting and people were running like hell," said the 25-year-old cameraman, who did not want to be identified for fear of reprisal.

The city's businesses had all shut down.

"It's a ghost town," he said.

Though he said he was frightened, he predicted that demonstrations would resume Saturday.

"It's better to die than to live without freedom," he told CNN's Anderson Cooper.

Ted Kattouf, the former U.S. ambassador to Syria, expressed admiration for the demonstrators' courage, but made no predictions about where it might lead.

"Unfortunately, repression, if used repeatedly, ruthlessly, brutally, can work. We saw that in Iran and, I'm afraid, we could see it in Syria."

The demonstrators do not have the critical mass needed to effect regime change, Kattouf said. He noted that massive demonstrations have yet to appear in Damascus or Aleppo, where millions of people reside, most of them Sunni.

President Bashar al-Assad is Shia.

"There's a coalition of interests here, and the demonstrations would have to get much, much larger and stretch the capacity of the regime's security services to the point where some people thought about maybe making their own ways and abandoning Assad."

The violence prompted international condemnation, with British Foreign Secretary William Hague calling the killings "unacceptable," and calling on Syrian security forces "to exercise restraint instead of repression, and on the Syrian authorities to respect the Syrian people's right to peaceful protest."

Before Friday's marches, Amnesty International and Human Rights Watch said the death toll had exceeded 200 since the demonstrations began in mid-March.

U.S. President Barack Obama condemned the use of force by the Syrian government against demonstrators.

"This outrageous use of violence to quell protests must come to an end now," he said in a statement. "The Syrian people have called for the freedoms that all individuals around the world should enjoy: freedom of expression, association, peaceful assembly, and the ability to freely choose their leaders. President Assad and the Syrian authorities have repeatedly rejected their calls and chosen the path of repression."

He accused Assad of "blaming outsiders while seeking Iranian assistance in repressing Syria's citizens through the same brutal tactics that have been used by his Iranian allies."

U.N. Secretary-General Ban Ki-moon and the spokesman for France's Ministry of European and Foreign Affairs condemned the violence.