(CNN) -- Escalating violence between Syrian security forces and anti-government protesters claimed 15 people Wednesday in the city of Daraa, witnesses and rights activists said. Syrian state television reported the government fired the governor of Daraa province, a flash point of anti-government protests.
There was no breakdown on the casualties. According to activists and witnesses, seven people died shortly after dawn prayers near al Omari mosque. Security personnel tried to storm the area where protesters took positions to demand government reforms, an opposition spokesman said.
Later, about 3,000 protesters from neighboring towns gathered outside Daraa and clashed with an army unit known for its loyalty to President Bashar al-Assad, activists and witnesses said. The army unit is headed by a family member, Maher al-Assad, said the opposition spokesman.
Eight more people died in the later clashes, bringing the death toll Wednesday to 15, according to the sources. Overall, at least 21 people have died in unrest in the city since Friday.
Army tanks are positioned in the city, including near al Omari mosque, the opposition spokesman said. Mobile and regular telephone service from Daraa has been cut off, witnesses told CNN.
Wissam Tarif, executive director of the human rights group Insan, told CNN from outside Damascus that Syrian security forces fired live ammunition at unarmed protesters.
He said he was aware of three protesters killed in the clashes, but added there was no information on the injured because people don't go to the hospitals anymore. This is because some disappeared after being taken for treatment earlier in the unrest, he said.
According to Tarif, demonstrators want an end to the decades-old state of emergency in Syria, the release of prisoners of conscience and more freedoms.
Syria is the latest in a string of Arabic-speaking nations beset with discontent over human rights issues.
"The United States is deeply troubled by violence and civilian deaths in Daraa at the hands of security forces," State Department spokesman Mark Toner said in a statement Wednesday.
His statement expressed U.S. condemnation for what it called "the Syrian government's use of violence, intimidation and arbitrary arrests in Daraa to hinder the ability of its people to freely exercise their universal rights.
"We call on the Syrian government to exercise restraint and refrain from violence against peaceful protesters," Toner's statement said.
A witness who did not want his name used out of concern for his safety said security forces shot into the crowd in front of the al Omari mosque before daybreak Wednesday. The witness also said he heard an explosion.
Syrian state TV, however, said armed groups had attacked security forces, killing a doctor, a medical assistant and an ambulance driver.
Assad later issued an order to dismiss Daraa's governor, Faisal Kulthoum, from his position, Syrian state TV reported.
The violence comes a day after Syrian authorities arrested a prominent rights leader as anti-government demonstrations continue throughout the country's south.
Loay Hussein, a political prisoner from 1984 to 1991, was taken from his home in the Sehnaya district near Damascus on Tuesday, according to the country's Observatory for Human Rights.
Hussein had been supporting protesters who marched for a sixth straight day Tuesday, chanting, "The people want to bring down the regime," a spokesman for the organizers told CNN from Daraa.
The organizers are also planning a day of mass protests Friday, the spokesman said.
On Monday, protesters marched in Daraa after they buried the body of a protester who was killed Sunday in clashes between anti-government demonstrators and security forces, a witness told CNN.
Sunday's protests came the same day a delegation sent by the president offered "condolences to the families of the two martyrs who died during the unfortunate events which took place in Daraa on Friday," according to SANA, the Syrian news agency.
Local tribal leaders have said they rejected a government proposal to bring about calm and have put together a list of demands, including asking that the head of the local police and governor of Daraa be held accountable for the civilian casualties since Friday, witnesses said.
On Tuesday, the United Nations Human Rights office reported that six people have been killed by security forces in Daraa since Friday, calling for an "independent, transparent and effective investigation into these killings."
"The use of excessive force constitutes a clear violation of international law, which provides for individual criminal responsibility for violations committed," said Rupert Colville, spokesman for the U.N. Office of the High Commissioner for Human Rights.
"People have the legitimate right to express their grievances and demands to their government, and we urge the Syrian government to enter into a broad, meaningful dialogue with the protesters in an attempt to address those grievances," he said.
CNN's Tim Lister and Amir Ahmed contributed to this report