By Elizabeth A. Kennedy And Diaa Hadid

BEIRUT – Syrian army units have clashed with each other over following President Bashar Assad's orders to crack down on protesters in Daraa, a besieged city at the heart of the uprising, witnesses and human rights groups said Thursday.
More than 450 people have been killed across Syria — about 100 in Daraa alone — and hundreds detained since the popular revolt against Assad began in mid-March, according to human rights groups.
While the troops' infighting in Daraa does not indicate any decisive splits in the military, it is significant because Assad's army has always been the regime's fiercest defender.
It is the latest sign that cracks — however small — are developing in Assad's base of support that would have been unimaginable just weeks ago. About 200 mostly low-level members of Syria's ruling Baath Party have resigned over Assad's brutal crackdown.
Ausama Monajed, a spokesman for a group of opposition figures in Syria and abroad, said the clashes among the soldiers have been happening since Monday.
"There are some battalions that refused to open fire on the people," Monajed told The Associated Press, citing witnesses on the ground in Daraa, a city of 75,000 near the Jordanian border. "Battalions of the 5th Division were protecting people, and returned fire when they were subjected to attacks by the 4th Division."
The 4th Division is run by the president's brother, Maher.
The reports were corroborated by three witnesses in Daraa and an activist contacted by the AP. All four asked that their names not be used for fear of reprisals.

One of the witnesses said soldiers fired at each other Thursday around the Omari mosque in central Daraa. He said the soldiers from the 5th division, composed mostly of conscripts known to be sympathetic to residents, were battling soldiers of the 4th Division.
"They are defending the people against the forces of Maher Assad," said the resident, who said he lived next to the mosque and witnessed the battles.
"Assad's forces have it in their heads that we are terrorists and extremist Muslims and they are out to get us," he said. "But the 5th Division are made up of people like us. We are speaking to them."
Another witness in Daraa told the AP that he saw soldiers from different army units clashing Monday in front of the Bilal mosque, when Syrian forces rolled into town. He said the battle between the forces lasted for several hours.
"We saw ordinary soldiers fall," the resident said. "And then I heard people shout 'God is great! They are martyrs of freedom!'"

The military released a statement Wednesday denying there were any splits.
The government has blamed armed thugs and a foreign conspiracy for the unrest, rather than true reform seekers. State-run Syrian TV has been running lingering, gruesome close-ups of dead soldiers to back up their claims that they were under attack.
On the diplomatic front, Turkey held out the prospect of closer economic ties if Assad meets demands for reform, even as Western powers warned of sanctions if the crackdown doesn't end. Assad met a delegation led by the chief of Turkey's National Intelligence Agency and the head of the agency that oversees infrastructure projects, Turkey's Anatolia news agency reported.

Turkish Prime Minister Recep Tayyip Erdogan, who has talked to Assad at least three times since protests began in Syria, said Turkey does not want to see an "an authoritarian, totalitarian, imposing structure" there. But he has not called for Assad's ouster.
Syria is a highly unpredictable country, in part because of its sizable minority population and the regime's web of allegiances to powerful forces including Lebanon's Hezbollah and Shiite powerhouse Iran. Serious and prolonged unrest are likely to hurt the regime's proxy in Lebanon, the militant group Hezbollah, and weaken Iran's influence in the Arab world.
But within Syria, there are very real fears of sectarian bloodshed should a power vacuum emerge. Syria has multiple sectarian divisions, largely kept in check under Assad's heavy hand and his regime's secular ideology. The majority of the population is Sunni Muslim, but Assad and the ruling elite belong to the minority Alawite sect, an offshoot of Shiite Islam.
There are fears that if the regime falls, there could be revenge attacks and persecution as rival groups jockey for power.

For now, Assad is facing the gravest challenge to his family's four decades of rule. He unleashed the military, backed by snipers and tanks, in Daraa and several other areas Monday.
Daraa was the hardest-hit: On Thursday, more soldiers in armored personnel carriers rolled into Daraa, where residents huddled inside homes to avoid blasts of mortars and heavy gunfire. Hiding from snipers perched on rooftops, desperate Syrians pleaded for international help Thursday as a military siege paralyzed the city.
The protest movement insisted it will not be intimidated and used the crackdown in Daraa as a rallying cry to encourage fresh demonstrations across the country Friday.
Syria has banned nearly all foreign media and restricted access to trouble spots since the uprising began, making it almost impossible to verify the dramatic events shaking one of the most authoritarian, anti-Western regimes in the Arab world.

Daraa resident Abdullah Abazeid said the death toll in Daraa includes a 6-year-old girl, hit by a sniper Wednesday on the roof of her parents' apartment. He added that pro-government gunmen known as "shabiha" damaged a large numbers of shops in the city.
Abazeid said they were still hiding the bodies of the dead because the cemetery was occupied by Syrian forces.
The city was still without telephones, electricity and water and lacked food and infant formula, he said, adding that some parents were giving their children water and sugar for lack of powder milk.
Later in the evening, there were reports that power had been restored.
Meanwhile, Syrians were pouring into the neighboring countries of Lebanon and Jordan seeking refuge from the violence. A woman in Jordan whose family lives in Daraa said she heard her two brothers had been killed.
She said she came to the border to tell her story to the media, but her husband and female members of his family dragged her away, screaming.
Elsewhere in Syria, security was tightened in the Damascus suburb of Douma and the coastal city of Latakia, the heartland of Syria's ruling elite.
"Security is so tight around Douma that even birds can't go in," he said, adding that security forces with lists of wanted people continued to detain residents in the area.
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Hadid reported from Cairo. Associated Press writers Jamal Halaby at the Jordanian-Syrian border, and Christopher Torchia in Istanbul contributed to this story.