US President Obama warned Syria on Monday that it would face American military intervention if there were signs that its arsenal of unconventional weapons was being moved or prepared for use. It was Mr. Obama’s first direct threat of force against Syria, as he has resisted being drawn into the bloody 18-month rebellion.
The president’s warning raises the pressure on President Bashar al-Assad, whom Mr. Obama again called on to relinquish power. And it underscores the deepening alarm among American officials that, as Syria sinks further into civil war, its unconventional weapons could be seized by radical forces tied to terrorist groups like Hezbollah in Lebanon or Al Qaeda.
The warning brings Mr. Obama, who has brushed aside calls to impose a no-fly zone or to arm the Syrian rebels, a step closer to direct American engagement. The specter of unconventional weapons being loosed in the heart of the Arab world, he said, would upend his calculation that military intervention would only worsen the situation.
“We cannot have a situation in which chemical or biological weapons are falling into the hands of the wrong people,” Mr. Obama said in response to questions at an impromptu news conference at the White House. “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.”
“That would change my calculus,” he added. “That would change my equation.”
Western authorities say that Syria’s arsenal includes chemical weapons but that they are uncertain whether the country has stockpiled biological weapons.
The president said the Pentagon was drafting a range of contingency plans, working with American allies in the region, including Israel and Turkey. He expressed little confidence that the Syrian government could keep its weapons stockpile under lock and key, given the widespread strife in the country.
Last month, American officials said they had unspecified evidence that Mr. Assad’s forces had moved some parts of the stockpile out of storage, although the transfer was never confirmed. Experts on Syria speculated at the time that the move reflected the government’s worry about the security of the weapons, not any intent to use them.
The Syrian Foreign Ministry announced in July that it would deploy chemical weapons only against foreign intervention, never against its own citizens.
A senior administration official emphasized that Mr. Obama’s warning was aimed at large-scale transfers of weapons that would make them vulnerable to capture by radical forces, not movements by the government intended to secure the arsenal.
The administration said it was monitoring suspected weapons sites, along with Turkey and Jordan, and has held discussions with Israel about how to respond to any breaches of security.
Mr. Obama, who has said little about Syria in recent weeks, stressed the regional risk from its unconventional weapons. “That’s an issue that doesn’t just concern Syria,” he said. “It concerns our close allies in the region, including Israel. It concerns us.”
His comments seemed aimed as much at the Israelis as the Syrians. Israeli officials have indicated they might intervene if they thought those weapons were on the loose and might be unleashed on their territory.
By hinting that the United States might participate in locating and neutralizing the weapons, Mr. Obama was clearly trying to forestall the possibility of an Israeli move into Syria — and the reaction it might provoke.
For weeks, Mr. Obama’s aides and outside advisers to the White House and Pentagon have been saying that if Syria’s presumed stockpiles of unconventional weapons got loose, only the United States and a small group of European allies would have the technological capability to neutralize them. That would almost certainly require the insertion of specialized teams, which would require considerable protection while operating inside Syria.
The Pentagon contingency plans include worst-case scenarios that would require tens of thousands of American troops, two senior United States officials said on Monday. The officials, who declined to specify precisely how many troops might be needed, emphasized that the plans were the kind of worst-case contingency options that the Pentagon routinely draws up in crises, and that no American deployments were imminent.
“The problem is that the material is so dispersed,” said an expert who has been consulted by the administration. While the intelligence about the stockpiles is sketchy — there are widely varying estimates of how much material Mr. Assad has amassed, and where it is stored — American estimates indicate there could be as many as two dozen sites around the country.
The difficulty in pinpointing Syria’s stockpiles is one of many complexities that have made Mr. Obama leery of getting drawn into the conflict. On Monday, he described a so far limited American response that includes $82 million in humanitarian aid to help thousands of Syrian refugees, as well as efforts to help the Syrian opposition prepare for a transition of power.
It was almost a year to the day since Mr. Obama first called on Mr. Assad to resign, and he was plainly frustrated by the lack of progress. “So far, he hasn’t gotten the message and instead has doubled down in violence on his own people,” Mr. Obama said.
In Syria, a Japanese journalist was killed Monday while covering the conflict in Aleppo, Japan’s Foreign Ministry said Tuesday, according to The Associated Press. The reporter, Mika Yamamoto, a veteran war correspondent, was hit by gunfire while she and a colleague were traveling with the rebel Free Syrian Army. Mr. Assad’s forces stepped up their attacks in and around the southwest city of Dara’a on Monday, with activists reporting raids, summary executions of suspected opposition figures and intensified shelling. There was no way to independently confirm those reports.