President Obama said Wednesday that the United States was investigating claims that chemical weapons had been used in Syria the day before and that he was ‘‘deeply skeptical’’ of the Syrian government’s assertion that the insurgency had deployed such weapons.
The president’s remarks were strong in tone and suggested that if Washington finds evidence that such weapons had been used he would hold the Syrian government responsible.
On more than one occasion Obama has said that the deployment of chemical weapons in the 2-year-old Syrian conflict would be a ‘‘red line’’ for the United States, which supports the opposition to President Bashar Assad but has not provided military aid to the rebels fighting him. Assad’s military is known to have large stockpiles of chemical arms.
Obama’s remarks, at a news conference in Jerusalem with Prime Minister Benjamin Netanyahu of Israel, were his first public reaction to the reports Tuesday that chemical weapons had been used in Syria. Both sides in the conflict have accused the other of responsibility but there has been no independent evidence that the weapons were used.
‘‘We intend to investigate thoroughly exactly what happened,’’ Obama said in response to a question. ‘‘I’ve instructed my teams to find out precisely what happened, what we can document, what we can prove.’’
‘‘I’ve instructed my teams to find out precisely whether this red line was crossed,’’ he said.
However, Obama continued, even though he does not have all the facts, ‘‘We know the Syrian government has the capacity to carry out chemical attacks.’’
He said he was ‘‘deeply skeptical of any claim that it was the opposition that used chemical weapons.’’
Obama spoke after both the Syrian opposition and the government had escalated their mutual accusations of chemical weapons use, with both sides demanding an international investigation.
The National Coalition of Syrian Revolutionary and Opposition Forces, the umbrella political group that wants to topple Assad, said in a statement that it ‘‘condemns these attacks and holds the Assad regime fully responsible for shedding Syrian blood.’’
The group said the attacks killed at least 19 civilians and left 69 others short of breath, with some in critical condition.
In a statement from its Cairo headquarters, the coalition accused government forces of carrying out two chemical weapons attacks Tuesday — one in the Khan al-Assal area of northern Aleppo Province, as originally asserted, and a second strike in the Ataybah area of suburban Damascus.
‘‘The coalition demands a full international investigation,’’ the statement said. ‘‘All evidence now indicates that the Assad regime is using these weapons against its own people.’’
At the United Nations, the Syrian ambassador, Bashar Jaafari, told reporters that his government had also requested an official inquiry to corroborate its claims that insurgents — not government forces — had used the weapons.
Jaafari said he had delivered a letter to UN Secretary General Ban Ki-moon’s office seeking a ‘‘specialized, independent and neutral technical mission to investigate the use by the terrorist groups operating in Syria of chemical weapons yesterday against civilians.’’
Ban’s spokesman, Martin Nesirky, said he had learned of the Syrian government’s request from Jaafari’s remarks.
“We will have more to say once we have received and studied any formal request,’’ Nesirky told reporters.
Nesirky also repeated Ban’s reaction to the first allegations of chemical weapons use Tuesday, saying, ‘‘The secretary general remains convinced that the use of chemical weapons by any party under any circumstances would constitute an outrageous crime.’’
Israeli officials, who have repeatedly expressed concern about chemical arms in neighboring Syria, suggested in their most recent comments that such arms were used Tuesday.
Yuval Steinitz, the newly appointed minister of intelligence and strategic affairs, told Israel’s Army Radio on Wednesday, ‘‘It’s apparently clear that chemical weapons have been used against civilians by the rebels or by the government.’’
US officials have been deeply skeptical that chemical arms were used but have not ruled out the possibility that Assad’s forces might have used them.