By MARIA ABI-HABIB

RAMTHA, JORDAN—Sitting among family in this Jordanian town on the Syrian border, an ex-army intelligence officer recounted how he worked against rebel forces by intimidating family members to prevent military defections.

Now he’s a defector.

At the start of the Syrian revolution a year ago, the 21-year-old said he sat in his barracks with colleagues and watched TV reports of widespread protests against the government that met with increasingly brutal crackdowns. One day, he said, the TVs were removed and his commanders told him and his colleagues they were fighting against terrorists aligned with the U.S. and Israel who were plotting to overthrow President Bashar al-Assad.

The intelligence officer said he worked tirelessly to crush the uprising in western Homs for five months, finally being granted two days of leave in July. He returned to his home in southern Deraa but it was riddled with bullets. His brother had been arrested under the charge of “protesting” and his cousin killed by bullets fired by Syrian troops while demonstrating, he and his family members said in interviews.

The officer then realized he hadn’t been fighting terrorists, but his own people, he said.

“I have innocent blood on my hands,” he said, staring at the floor as his 3-year-old sister played beside him and his father and brother smoked cigarettes.

The intelligence officer was interviewed here in Ramtha, a poor city of whitewashed apartment buildings, and home to many of the 95,000 Syrian refugees that Jordan says have left Syria since the uprising began. Other defectors remain in Syria.

Many diplomats say the prospects are bleak for the opposition to topple Mr. Assad—who activists say continues his bloody crackdown even after a cease-fire began on Thursday—until more Syrian troops switch sides.

Analysts peg the number of defections at around 10,000 military members, out of about 304,000 active-duty troops.

This month several Gulf nations pledged to fund a pool of up to $40 million to pay defectors’ salaries and encourage them to turn their guns on the regime. But refugees say the fund—which hasn’t yet begun funding defectors—will have little chance of encouraging mass defections unless the international community can help secure the families of defected soldiers, police and security forces.

There are other reasons mass defections aren’t happening as fast as the opposition had hoped. These include the loyalty Mr. Assad enjoys from fellow Alawites, a minority Muslim sect in Syria, in the top levels of the government and military. Most of the defections come from the lower ranks, who are predominantly Sunni, members of Syria’s majority population.

Also, the military is structured in a way that limits communication among different units, heightening the challenge of coordinating against Mr. Assad, said Ayham Kamel, an analyst at the Eurasia Group.

“The funds from the Gulf represent a catalyst for broader defections, but they are unlikely to produce results overnight or even in a short period of time,” Mr. Kamel said. “And the bulk of ammunition and heavy weapons are held by units most loyal to the regime.”

Still, some soldiers have remained in service as undeclared rebels within the system, diplomats and several Syrian refugees interviewed in Jordan say. At great risk, these soldiers inform the opposition of the military’s movements and wave rebels through checkpoints.

Here in Ramtha, a former lieutenant colonel recounted his swift—and short-lived—decision to desert the Syrian police and join rebel forces.

“I fought until they locked up my father, interrogated my sisters and burned down my house,” said the former officer, while sitting on floor cushions with other refugees. “Now that I’m no longer fighting and left Syria, the pressure on my family is less.”

He declined to provide contact details for his family inside Syria out of concerns for their security, and his story, like those of some other refugees, couldn’t otherwise be corroborated.

Elsewhere in Ramtha, a former soldier who escaped to Irbid, Jordan, near the Syrian border, said his brother defected from the Syrian air force in April only to be caught and arrested. When their father went to the prison to inquire about the brother, he too was locked up, the soldier said.

The rest of the family is too scared to ask after the father and son, worried they too will be jailed, the former soldier said.

“No country is providing us weapons, Saudi and Qatar say they want to, but don’t,” said the former solider, 29 years old. “If the West doesn’t help us or other Arab countries, we’ll go to Al Qaeda. We don’t want to accept them, but what can we do when our children are being killed?”

The intelligence officer said he followed his father here in December after being stationed in western Homs province.

Worried, the intelligence officer would call his family in Deraa—a southern province where antiregime protests started early last year—asking if they were keeping safe from terrorist attacks. Concerned the phones were tapped, the intelligence officer’s family would respond vaguely and hurriedly hang up. “All I could think about was that I had to leave the army,” he said. “But I had to secure my family first.”

Meanwhile, the army intelligence officer’s Deraa experience embittered him to the Assad regime, and when he returned to Homs in July, he said he became an informant, telling rebels about military operations.

In December, he told his superiors that a family member was ill, and returned to Deraa. He then fled to Ramtha after securing his family, who now lives in a cramped three-room apartment there with his sister’s husband and small child.

He said that what especially haunts him is the intelligence he provided to colleagues to arrest defectors’ female family members, a way to pressure the former soldiers to turn themselves in. He said he heard reports of rape perpetrated by his colleagues as another form of intimidation against family members, but hadn’t seen any firsthand.

“I defected because of what I saw how they killed people, like my own cousin, and destroyed their houses,” he said. “I decided I couldn’t do this.”

Write to Maria Abi-Habib at maria.habib@dowjones.com