WASHINGTON - US spy agencies face a difficult task in tracking Islamic jihadists in Syria, as Washington lacks a robust network of informants and faces threats to its drone fleet, experts and former officials say.
If President Barack Obama opts to expand air strikes against the IS militants from Iraq to neighbouring Syria, the effort could be delayed or hindered by intelligence gaps, former White House officials and analysts said.
Unlike in Pakistan's tribal areas, or in Iraq, the United States has been largely absent in Syria for years and has not built up a web of relationships that it could use to monitor the movements of IS senior figures.
"We don't have the same resources in Syria, we don't have the same intelligence resources that we do in Iraq," said Representative Adam Schiff, a Democrat from California.
"We don't have the same government we can work with in Syria," he told CNN.
"So the limits are much more substantial in Syria."
Informants and drones
American bombing raids in Iraq, Afghanistan, Pakistan and Yemen rely on numerous informants and a fleet of drones that can linger in the air for hours, waiting for senior militants to appear in their sights, ex-officials said.
In comparison, the US faces conditions in Syria where it is practically blind, one former official said.
"It's a daunting challenge. It's easier said than done," said Michael Rubin of the American Enterprise Institute, a Washington think tank.
With the withdrawal of US combat troops from Iraq, and a cautious approach to the civil war raging in Syria, America lacks a precise picture of its IS adversaries there, according to Rubin.
"We've let our guard down." In countries such as Pakistan, when intelligence reports indicate a senior Al-Qaeda figure may be expected in an area, US informants are able to stake out the location until the leader shows up, he said.
But in Syria, "we don't have that sort of network." Members of moderate Syrian rebel groups reportedly have been recruited as CIA informants but it appears to be a relatively small network compared to what the Americans developed in Pakistan over the past decade.
Washington must also contend with allies such as Turkey and Qatar that have different agendas and may not share the intelligence they have on IS, said Rubin.
The two governments have supported hardline elements in Syria and are playing "a double game," Rubin said, though Turkey and Qatar deny forging links to IS.
Obama has given the green light to surveillance flights inside Syria but it remains unclear if American drones and other aircraft face a serious threat from the Syrian regime's air defences.
Damascus has lost control of eastern parts of the country and analysts say its air defences would not be operational there.
Syria's Russian-made anti-aircraft missiles and radar, especially batteries around Damascus, were cited last year as cause for concern when Obama weighed possible military action against President Bashar al-Assad's regime.
And regime leaders may be reluctant to allow American spy planes to venture beyond the eastern border area to get a detailed look at Syrian forces and positions elsewhere.
Drones at risk?
Apart from regime air defences, US drones such as robotic Reapers and Predators could fly at high altitude and face only a "minimal" danger from IS militants' shoulder-launched weapons, according to Huw Williams, an analyst at IHS Jane's consultancy.
"Essentially, if Syrian air defences aren't targeting US UAVs (unmanned aerial vehicles), then technically they shouldn't have too many problems in operating against IS forces and employing the same surveillance packages and weapons as they do elsewhere," Williams said.
With the United States possibly poised to bomb a major foe of the Assad regime, it is unlikely Damascus would fire surface-to-air missiles on American warplanes and risk triggering US retaliation, said Gary Samore, a former senior adviser to Obama on arms control.
"I don't know why in the world the Syrians would want to interfere," said Samore, now at Harvard University's Belfer Center of Science and International Affairs.
"I would think the Syrian government would welcome those air strikes," he said. "Although they might protest them the way the Pakistani government does." For Samore, the bigger problem is the need for ground troops in Syria who can seize territory from IS militants in the wake of any bombing raids.
"The question is whether or not there are ground forces in eastern Syria that could follow up on US air strikes and actually control territory," he said. "The answer may very well be 'no.'"