Beirut ? Mass protests calling for sweeping changes in Syria’s authoritarian regime turned deadly Friday, with the government and protesters both claiming heavy casualties as the country’s three-week uprising entered a dangerous new phase.

The bloodiest clashes occurred in the restive city of Daraa, where human rights activists and witnesses said Syrian security forces opened fire on tens of thousands of protesters, killing 25 people and wounding hundreds.

At the same time, state-run TV said 19 policemen and members of the security forces were killed when gunmen opened fire on them. It was the first significant claim of casualties by the Syrian government, which has contended that armed gangs rather than true reform-seekers are behind the unrest — and it could signal plans for a stepped-up retaliation.

The protests were in response to calls by organizers to take to the streets every Friday to demand change in one of the most rigid nations in the Middle East. Marches were held in cities across the country as the movement showed no sign of letting up, despite the violent crackdowns.

At least 32 protesters were killed nationwide, according to human rights activists. The bloodshed lifted the death toll from three weeks of protests to more than 170 people, according to Amnesty International.

U.S. President Barack Obama in a statement Friday night condemned the violence and called on Syrian authorities to refrain from attacks on peaceful protesters.

“Furthermore, the arbitrary arrests, detention, and torture of prisoners that has been reported must end now, and the free flow of information must be permitted so that there can be independent verification of events on the ground,” he said.

The calls for reform have shaken the regime of President Bashar Assad, whose family has ruled Syria for more than 40 years. Assad, a British-trained eye doctor, inherited power from his father 11 years ago and tried to help the country emerge from years of international isolation and lift Soviet-style economic restrictions.

But despite early promises of social and political change, Assad has slipped back into the autocratic ways of his father.

As the wave of protests have gathered steam, Assad has offered some limited concessions — firing local officials and forming committees to look into replacing the country’s despised emergency laws, which allow the regime to arrest people without charge. On Thursday, he granted citizenship to thousands of Kurds, fulfilling a decades-old demand of the country’s long-ostracized minority.

But those gestures have failed to mollify a growing movement that is raising the ceiling on its demands for concrete reforms and free elections.

“The protests are about Syrians wanting freedom after 42 years of repression,” said Murhaf Jouejati, a Syria expert at George Washington University.

“Mr. Assad may fire all the people he wants, this still doesn’t touch on the basic issues and the basic demands of the protesters.”