The Obama administration froze the U.S. assets of Syrian Foreign Minister Walid al-Moualem and two other senior Syrian officials on Tuesday in response to Syria's increasingly violent crackdown against anti-government protesters.
The Treasury Department also named Syria's Ambassador to Lebanon Ali Abdul Karim Ali and President Bashar al-Assad's adviser Bouthaina Shaaban.
"We are bringing additional pressure to bear today directly on three senior Assad regime officials who are principle defenders of the regime's activities," said David Cohen, Treasury's Under Secretary for Terrorism and Financial Intelligence, in a statement.
The new regulations also ban Americans from doing business with the Syrian officials.
Syrian security forces killed at least seven people, including a 13-year-old boy, as thousands of protesters poured out of mosques and marched through cemeteries Tuesday at the start of Eid al-Fitr, a holiday when pious Muslims traditionally visit graves and pray for the dead.
The three-day holiday marks the end of the holy month of Ramadan, a time of introspection that many protesters had hoped would become a turning point in the 5-month-old uprising. Instead, the government crackdown on dissent intensified and the conflict has become a bloody stalemate.
Protesters: 'We will not stop'
"They can shoot and kill as much as they want, we will not stop calling for regime change," an activist in Daraa told The Associated Press by telephone, asking for anonymity out of fear of reprisals.
Tuesday's bloodshed was in the southern province of Daraa, the central city of Homs and the capital, Damascus, and its suburbs. Amateur videos posted by activists online showed protesters calling for the downfall of the regime and even the execution of Assad — a sign of how much the uprising against Assad has grown in both size and anger over the past five months.
The uprising began with modest calls for reform in Syria, an autocratic state that has been ruled by the same family for more than 40 years. But as the government crackdown escalated, so too did the protesters' demands. Now, most protesters are demanding nothing less than the downfall of the regime.
In the northern province of Idlib, a few hundred protesters marched with flower wreaths decorated with the Syrian flag and pictures of dead relatives. Many shouted: "Bashar, we don't want you!"
The Local Coordination Committees, an activist network, said six protesters were killed in Daraa province and one in Homs. An activist in Daraa confirmed the six deaths in Daraa, saying four were killed in the village of al-Harra and two others in Inkhil.
The deaths in al-Harra included a 13-year-old boy, they said.
The London-based Syrian Observatory for Human Rights also reported heavy gunfire in the Qaboun district of the capital Damascus, with five people injured.
State-run news agency SANA said Assad performed Eid prayers in the Hafez Assad Mosque in the capital, named after Assad's father, who ruled Syria with an iron fist for three decades until his death in 2000.
UN: 2,200 killed in uprising
The U.N. says more than 2,200 people have been killed since the uprising erupted in March, touched off by the wave of revolutions sweeping the Arab world.
Meanwhile, a human rights group said it believed that at least 88 people, 10 of them children, have died in detention in Syria during five months of anti-government protests — a dramatic increase that coincides with the government's bloody crackdown.
Some of the victims were as young as 13, Amnesty International said. It said that in recent years the annual number of deaths behind Syrian bars has been about five.
"These deaths behind bars are reaching massive proportions, and appear to be an extension of the same brutal disdain for life that we are seeing daily on the streets of Syria," said Neil Sammonds, Amnesty International's researcher on Syria.
The government crackdown escalated dramatically at the start of Ramadan, when Muslims typically gather in mosques during the month for special nightly prayers after breaking the dawn-to-dusk fast.
The Assad government used deadly force to prevent such large gatherings from turning into more anti-government protests.
The LCC activist network said Syrians were keeping their Eid celebrations to a minimum this year in solidarity with the Syrians who have died and the families of detainees.
"There will be no happiness while the martyrs' blood is still warm," it said in a statement Tuesday.
The Syrian government has placed severe restrictions on the media and expelled foreign reporters, making it nearly impossible to independently verify witness accounts.