As the White House mulls whether Syria has crossed President Obama’s red line and used chemical weapons, the U.S. military and intelligence community are quietly acknowledging that the United States does not know where many of those weapons are located.

The judgment comes from top U.S. military commanders and is supported by recent intelligence community assessments, according to three U.S. officials who work closely on Syrian intelligence matters. At the heart of the concern is that the Syrian military has transferred more and more of its stock of sarin and mustard gas from storage sites to trucks where they are being moved around the country. While U.S. intelligence agencies first saw reports that Syria was moving the weapons last year, the process has accelerated since December, according to these officials. Also worrisome, said two of the officials, is intelligence from late last year that says the Syrian Scientific Research Center—an entity responsible for Syria’s chemical-weapons stockpile—has begun to train irregular militias loyal to Syrian President Bashar al-Assad in how to use the chemical munitions.

The assessment that Syria is moving large amounts of its chemical weapons around the country on trucks means that if Obama wanted to send in U.S. soldiers to secure Syria’s stockpiles, his top generals and intelligence analysts doubt such a mission would have much success, according to the three officials. “We’ve lost track of lots of this stuff,” one U.S. official told The Daily Beast. “We just don’t know where a lot of it is.”

The large-scale movement of weapons, if it is in fact occurring, would violate one of Obama’s earliest declared red lines concerning Syria. Last August he said, “We have been very clear to the Assad regime, but also to other players on the ground, that a red line for us is, we start seeing a whole bunch of weapons moving around or being utilized.”

The recent assertions from U.S. officials build on statements made last month by chairman of the Joint Chiefs of Staff Martin Dempsey and Director of National Intelligence James Clapper. After being asked by Sen. John McCain on April 17 if he had confidence that the United States could secure the stocks of chemical weapons in Syria, Dempsey initially expressed vague confidence. But after McCain pressed him on this point, he could not give the assurance McCain wanted: “Not as I sit here today,” he said, “simply because they have been moving it, and the number of sites is quite numerous.” A week earlier, Clapper had also told Congress that he did not know if the United States could secure Syria’s chemical weapons. “It would be very, very situational dependent to render an assessment on how well we could secure any or all of the facilities in Syria,” he said.

These remarks struck a different tone from the one top Obama officials had put forward last year. Leon Panetta, Obama’s last secretary of defense, acknowledged in September that there had been “limited movement” of chemical munitions, but he said that “the major sites still remain in place.”

Meanwhile, not all U.S. officials agree with the worrisome intelligence assessments recently relayed by the three officials. “Any effort to secure Syria’s chemical-weapons would be complex, but we have good visibility on Syria’s chemical-weapons stockpiles and are constantly monitoring for any sign of movement,” a White House official told The Daily Beast late Wednesday. “We believe that the stockpiles are secure.” (A spokesman for the director of national intelligence declined to comment for this story Wednesday.)

But other U.S. officials said one of the problems in tracking the chemical stocks in Syria once they were loaded onto trucks was finding out where those trucks were headed. One official said U.S. spy satellites in November picked up clear photographic evidence of trucks being loaded at known chemical-weapons storage sites outside Damascus. But this official also said the satellite did not track the movement of the trucks in the country. “You have to remember that satellites are not unmanned aerial vehicles,” this official said. “We saw the trucks being loaded, but we did not see where they went.”

Meanwhile, the intelligence assessment that irregular militias are being trained in chemical warfare presents another problem—in part because the intelligence community had launched an ambitious plan to communicate directly with the midlevel Syrian officers in charge of chemical weapons to dissuade these officers from launching a chemical attack. “We don’t know much about who the loyalists are,” the U.S. official said.