Syrians who took to the streets Friday after prayers knew they were defying threats from their president.

But they poured out anyway, tens of thousands of them, calling for his ouster a day after he lifted a set of despised emergency laws. And in towns and cities across the country, President Bashar al-Assad’s security forces answered with guns.

By late Friday, 81 people were confirmed dead, said Wissam Tarif, director of a Syrian human rights group. In at least 10 towns and cities, activists and witnesses said, government forces shot into crowds, beat protesters with batons and Kalashnikovs, and used tear gas against them.

It was the biggest single-day death toll in Syria’s six-week-old uprising, and it offered no sign that the Damascus government might give in to swelling demands for democratic change. Unlike the authoritarian governments in Tunisia and Egypt that fell quickly in this year’s Arab revolutions, the Syrian authorities appear to retain tight control over the army and police.

On Saturday, thousands of mourners shouted slogans and demanded the overthrow of the Assad government at funerals across Syria for those killed during the protests.

In Washington, President Obama made his toughest statement to date on the situation in Syria, condemning the use of force “in the strongest possible terms” and calling on Assad to “change course now.”

For the first time, Obama directly blamed the Syrian president for the crackdown, saying Assad had placed his “personal interests” ahead of his people, and tied Syrian repression to Iran. But Obama stopped well short of calling on Assad to cede power. While his statement marked a sharp escalation in tone, it offered no indication that further U.S. action was being contemplated.

Late Friday, an administration official said that the White House was “looking at a range of possible responses to this unacceptable behavior” but declined to provide details. Among the options available are recalling the U.S. ambassador in Damascus — just months after the job was filled following a five-year vacancy — and removal of waivers granted on several trade items in recent years. Appeals could be made to the European Union, Syria’s largest trading partner, to adopt sanctions, and broader condemnation could be sought through the United Nations.

The state-run Syrian Arab News Agency, SANA, reported only that “limited numbers” of demonstrators had taken to the streets and that security forces and police used “hoses and tear gas to settle scuffles’’ between protesters and citizens. It said eight people had been killed in a gunfight involving “masked individuals who opened fire” on military personnel.

Despite the bloodshed Friday, protesters showed no signs of stopping, and the demonstrations spread to cities including Homs and Qamishli, and to the suburbs of Damascus despite tanks and checkpoints stationed across the country to control them. Most foreign journalists have been expelled from the country, but accounts of the violence were provided by activists and other witnesses, along with images posted on YouTube that showed dead bodies and people in army uniforms shooting.

The number of dead and wounded was expected to rise, said Tarif, whose rights group is known as Insan, the Arabic word for human. The heaviest tolls reported were in the town of Izra, in the Daraa region, with 26 dead, and in Homs, with 14, Tarif said. Homs was the site of crackdowns earlier this week that left as many as two dozen people dead.

An ally of Iran and a supporter of Hezbollah, Syria is made up of Sunnis, Christians, Druze and Alawites, who practice a form of Shiism that is the faith of the ruling family. Assad’s government has blamed the violence on foreign provocation, and has warned that any destabilization of the regime will open the door to extremist Islamists.

The protesters in Syria are still a minority, with most people staying home out of loyalty to the regime, fear of reprisals or trepidation about what a post-Assad Syria could look like. But protests were expected to swell again Saturday, continuing what has become a weekly cycle, as people counted the bodies and buried the dead.

The protesters have taken to the streets in increasing numbers each Friday since the demonstrations began, turning out after Muslim prayers. In early weeks they demanded reforms; later, they began demanding the overthrow of the regime, dismissing as inadequate concessions made by Assad, including the lifting of emergency laws. Rights groups estimate that 300 Syrians have been killed in the six weeks of violence.

Interviewed via Skype on Friday, a demonstrator in the Damascus suburb of Harasta said he saw three people die when security forces opened fire on a group of about 3,000 people carrying olive branches and proclaiming a brotherhood of Christians, Muslims, Alawites and other religious groups. The shooters, wearing army uniforms, fired without warning, and continued to pursue and fire on people as they fled, the demonstrator said.

“I cried a lot,” the demonstrator said, asking that his name be withheld for fear of reprisals. “After they have spoken about lifting the emergency law, how could they shoot people this way?”

At midday prayers in the city of Daraa, an imam had his own warning for the government, one witness said.

“He was telling people that they should take care of the country, just be peaceful, that they shouldn’t ruin their country,” said Adnan Mahameed, 35, a travel agency employee who attended the prayer and said the imam seemed to be directing his comments at security forces who might be present.

Calling the government’s promises false, Mahameed added, “We feel like we’re slaves on a farm; we have no rights, but we’re living here. It’s not a normal life.”

Obama administration officials have said repeatedly that they have little leverage in Syria, where U.S. sanctions already prohibit aid and most trade, and U.S. regional allies have expressed more concern about future chaos in the strategically positioned Arab state than they have about Assad’s crackdown.

Obama has been reluctant to denounce Assad in the forceful terms he used in publicly telling Egypt’s Hosni Mubarak, weeks after street demonstrations began in Cairo, to begin transitioning out of power “now.” In Libya, he has demanded that Moammar Gaddafi step down and leave the country, and sent U.S. warplanes to reinforce the message.

But the statement on Syria that was issued by the White House on Friday carried a sharp new tone. In it, Obama said that Assad was “blaming outsiders while seeking Iranian assistance in repressing Syria’s citizens through the same brutal tactics that have been used by his Iranian allies” to quell domestic protests in that country.

Assad, 45, was trained in Britain as an ophthalmologist and took over in 2000 after the death of his father, Hafez al-Assad, who held power for 30 years.

Thirteen Arab human rights groups signed a statement Friday criticizing the Arab League for adopting “double standards’’ in its support for Syria, a member of the organization. The statement accused the league of showing “disregard for the feelings and rights of the Syrian people, who have broken the barrier of fear and risen up in revolt.’’ It was signed by nongovernmental groups advocating for human rights in Egypt, Bahrain, Algeria, Saudi Arabia, Yemen, Syria, Sudan and Iraq.

The statement was directed toward the Arab League’s decision to endorse Syria’s candidacy for a seat on the U.N. Human Rights Council in a vote set for May. “It seems as if the League of Arab States is rewarding the regime for its repression,” the statement said.

Staff writer Karen DeYoung in Washington and special correspondent Danna Yunis in Beirut contributed to this report.