As Syrian rebels from across the political spectrum went on the attack against the extremist Islamic State of Iraq and Syria early last month, ISIS’s comrades in arms in the nearby province of Latakia didn’t miss a beat in their strange mode of war. They attacked three civilian hospitals.

In Rabiaa, a village in northwest Latakia, 15 ISIS gunmen arrived in three cars, arrested moderate rebel guards protecting the building and then stormed the hospital, according to Brig. Gen. Ahmad Rahal, who commanded the moderate rebels.

Hospital staff helped two wounded moderate rebels escape to the nearby al Yamdiah hospital. The ISIS gunmen followed them there. Then they stormed that hospital, killing one wounded rebel and abducting the second, Rahal said. The staff closed the hospital in protest, and ISIS later handed back the patient.

Meanwhile, ISIS forces attacked the al Biranas hospital, run by the Belgian branch of Doctors Without Borders, where they abducted five foreign doctors: from Belgium, Denmark, Peru, Sweden and Switzerland. All are still missing.

In the midst of the melee, a day after ISIS gunmen took over the guard posts at Rabiaa, the Syrian army bombed and destroyed the Rabiaa hospital, Rahal said.

Why ISIS was attacking hospitals in Latakia when its own forces were being besieged elsewhere in the country by other rebel factions is unclear. It may have been a sign that its commanders were confused about what was going on or that local commanders were unaware of what was taking place elsewhere. Or it could have been another example of the strange priorities of the Iraq-based movement that until recently had been viewed as part of the rebellion against Syrian President Bashar Assad.

Not until late last year did a pattern emerge of ISIS attacking “soft” targets. In the final months of 2013, ISIS increasingly raised anger as it abducted doctors, reporters, media activists and aid workers and closed down hospitals and media offices. By late last month, ISIS forces had set up so many checkpoints that they could halt the movement of people and goods across the Turkish border, including arms for other rebel forces.

The pattern of ISIS assaults is a controversial aspect of its move from Iraq to becoming a dominant force in the Syrian rebellion. Moderate rebels say it suggests a relationship between ISIS and the Syrian government. Others, including U.S. officials, say they think ISIS is pursuing its own agenda, which just happens to benefit the Assad government.

ISIS’s emergence “and its determination to sow discord within the opposition must have prompted celebration among Syrian regime officials,” conceded a U.S. official who follows the situation in Syria, who spoke only on the condition of anonymity because of the sensitivity of the subject. But he said the United States doubted there was a relationship between the two, and speculated that as long as ISIS was focused on attacking other rebels, “the regime may have reason to treat the group with kid gloves.”

“They are benefiting from its tactics,” the official said.

That leaves some odd situations. At Ad Dana, for example, a town on the Syrian-Turkish border that ISIS turned into its command center, the group set up in the municipal building, raising an enormous black flag outside. Only one part of the town was not under ISIS control: the hospital, about 500 yards away, guarded by forces who’d declared themselves part of the moderate Free Syrian Army. On Dec. 23, a Syrian jet bombed the hospital, destroying the emergency wing and killing a doctor and a nurse, according to aid organizations and local activists.

Officials of three Syrian medical associations said ISIS had stormed a number of hospitals in past months, seizing or assassinating patients and abducting medical personnel. Its drive against hospitals has led to an exodus of doctors from Syria, adding to an already severely strained health care system.

One official of a Syrian relief organization that operates in the country and claims to be neutral in the conflict said his group had suffered from both the government and ISIS. He asked to remain anonymous so that his comments wouldn’t affect his organization’s ability to work.

Last April, he said, his organization had attempted to send medical supplies to Ghouta, just east of Damascus, but came under attack from regime forces. “We lost 13 people: seven killed and six arrested,” he said. In November, his group organized a second aid shipment, and this time it was seized by ISIS in an attack that left one aid worker dead and one wounded.

ISIS also has targeted humanitarian aid workers. Six employees of the Geneva-based International Committee of the Red Cross and one employee of the Syrian Arab Red Crescent were abducted in northern Syria in October, and three of the seven are still being held. The action has frozen ICRC movements into northern Syria, and other aid agencies have largely followed suit.

The other major target has been journalists, both foreign reporters and Syrians working for news outlets or the anti-regime Local Coordination Committees, which issue reports on the day’s fighting.

The New York-based Committee to Protect Journalists said ISIS had become the “single biggest threat to journalists” in Syria. It counted 30 journalists missing.

ISIS publicly warned in September that any reporter caught crossing illegally into Syria across the Turkish border would be arrested and held indefinitely. From then, the number of abductions rose monthly, from two in September to four abductions and two assassinations in October and 11 abductions in November, according to a list compiled by the Union of Free Syrian Journalists, an opposition group. In December, there were 15 abductions, the group said.

Many of those arrested were seized in ISIS raids on the offices of their organizations. ISIS raided at least eight offices in December, often destroying or removing the laptops, printers and communication equipment, according to a list issued by the Syrian Network for Human Rights, an opposition organization.

ISIS, widely estimated to have as many as 6,000 fighters, deployed significant numbers to stage its raids. In an attack on a local radio station and the local news bureau in Kafr Nabul on Dec. 28, for example, ISIS deployed 20 gunmen, according to the station’s staff.

“They forced the activists to their knees, pointed their weapons and warned they would shoot if we didn’t respond to their demands,” one activist, identified only by his initials, A.A., said in a report published by the Syrian Network for Human Rights. Then they rampaged through the office. “They broke office equipment, stole documents … seized computers that we use at work, cameras, satellite Internet devices, all the while cursing and forcing us to grovel and put our hands up,” he said in a summary published by the network.

They arrested seven staff members but released them six hours later.

In a report issued late last month, the Syrian Network for Human Rights said that as a result of the murders of reporters or media activists, which it put at 13, and abductions, which it put at 38, a large number of journalists had fled the country.

Many of the abducted journalists and media spokesmen are still missing. ISIS gunmen killed an Iraqi photojournalist in early December, according to the Syrian guide who was with him at the time. Syrians also were killed while in detention. When ISIS abandoned its base at the Aleppo eye hospital early last month, four media personnel were found among the 50 people whom the group’s fighters had executed before they left the city.

Jonathan S. Landay contributed to this story from Washington.

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