WASHINGTON – Growing speculation that the Syrian regime is using chemical weapons is turning up the heat on President Barack Obama, who has warned such a move would be a game changer.

The U.S. administration, both in public and in private, says it has not concluded that such arms — of which President Bashar al-Assad’s regime has a large stockpile — have been employed in the bloody civil war.

But “it’s important that we do whatever we can to monitor, investigate and verify any credible allegations, given the enormous consequences for the Syrian people and given the President’s clear statement that chemical weapons use is unacceptable,” White House spokesman Jay Carney said Tuesday.

On March 20, during a historic visit to Israel, Obama said the use of such weapons would be a “grave and tragic” mistake on Assad’s behalf and that it would be a “game changer.”

Washington has also warned that any use or transfer of chemical weapons would cross a “red line” and possibly trigger military action.

Recent statements from U.S. allies seem to suggest such arms — illegal under international law — may already have been unleashed.

U.S. Secretary of State John Kerry leaves after a news conference at the NATO headquarters in Brussels April 23, 2013. Kerry said on Tuesday that NATO needed to consider its role in the Syrian crisis, including how practically prepared it was to respond to a potential chemical weapons threat. REUTERS

The latest came Tuesday when Israeli Brigadier General Itai Brun, head of the research and analysis division of military intelligence, alleged Assad’s regime had used chemical agents — mostly likely sarin gas — more than once.

His comments came on the heels of similar assessments reported to the United Nations by France and Britain last month.

Speaking on condition of anonymity, the official added that the use of chemical weapons in an environment like Syria was very difficult to confirm.

“Given the stakes involved, low confidence assessments by foreign governments cannot be the basis for U.S. action,” the official said.

U.S. Defense Secretary Chuck Hagel, on a visit to Cairo Wednesday, said any evidence had to be weighed carefully and said the U.S. needs to rely on its own intelligence. 

Analysts have said that different countries are coming up with different conclusions on whether or not the weapons had been used.

Syrian Foreign Minister Faisal Mekdad dismissed Western and Israeli claims that government forces had used chemical weapons, saying it was a “big lie” that Syria was blocking a U.N. investigation into the allegations.

He said Damascus had an initial agreement with the U.N. to look into claims that chemical weapons were used in the Khan al-Assal area near Aleppo but matters were complicated when the U.N. wanted to broaden the probe to include other allegations:

“We are ready to receive immediately the team to investigate the case of Aleppo, to provide all the logistics, help and support and protection and it is the responsibility of the U.N. secretariat if this delegation doesn’t arrive in Syria.”

A former Syrian ambassador to the United Nations, Mekdad accused Britain and France of trying to complicate the U.N. investigation to prevent evidence emerging of rebel use of chemical shells, but did not offer evidence for the allegation.

The United Nations wants inspectors to investigate claims of chemical weapons use in Homs in December; France and Britain say the mission should look into a third alleged case in Damascus.

President Barack Obama has warned Assad that deploying chemical weapons would cross a “red line” that could prompt the United States to intervene in unspecified ways in the conflict – so far, however, Washington has said firm evidence is lacking.

U.S. Secretary of State John Kerry (R) walks behind Russian Foreign Minister Sergei Lavrov (L) at the start of a NATO-Russia foreign ministers meeting in Brussels April 23, 2013.

Mekdad denied that Damascus was receiving arms and military support from Russia or fighters from Iran or Hizbullah, Tehran’s Lebanese Shi’a ally; foreign supporters were providing only humanitarian aid and Syria had ample reserves of its own.

“We are not isolated, we don’t feel isolated,” he said of efforts to impose international sanctions. “Besides Russia, we have China, India, South Africa and we have almost all Latin American countries, and Africa and other Asian countries.”

Mekdad reflected the government’s contention that Syria has been targeted by U.S.-allied Sunni Arab powers because it was part of “an axis of resistance”, along with Iran and Hizbullah, and accused Sunni-led states of secretly supporting Israel: “We believe the main objective in attacking Syria is to weaken it as a major power and to implement Israel’s policies in the region in connivance with the United States and Western interests.”

Asked how he believed the conflict would end, Mekdad sketched two scenarios: “Either we opt for a political solution as projected by President Assad in his speech on January 6 … or the other scenario where the main objective of arming, harboring and smuggling armed groups into Syria will continue.”

“In this case, we have a strong army, we have a strong country, we have determination by the majority of Syrians to combat terrorism. But our preference and the preference of the Syrian leadership is to work for a political settlement.”

Assad offered in that speech in January to negotiate with the opposition if they laid down their arms but he refused dialogue with “gangs recruited abroad” and his foes dismissed the offer out of hand as it did not mention Assad stepping down.

Syria’s army seized on Wednesday a key town east of Damascus after weeks of fierce battles against insurgents, a monitoring group said.

Otaybeh is important because it opens the way to Eastern Ghouta, a rebel stronghold east of Damascus that insurgents use as a rear base for infiltrating the capital.

Elsewhere, rebels battled regime troops inside the Minnigh military airport in the north of the country for the first time on Wednesday, the Observatory said.

On Tuesday, the rebels took a key military position outside the airport, in Aleppo province, which allowed them to launch a raid on it.

A group of regime-allied fighters who attempted to reach the airport to boost government troops there were intercepted by Kurdish fighters who killed nine of them, the Observatory said.

A military source said the rebels broke into the airport on Tuesday but added that they were then pushed back out.Rebel fighters have tried repeatedly to take the key airfield.

Since the beginning of the year, rebel forces have been fighting what they call the “battle of the airports in Aleppo” in a bid to deprive the regime of a key supply route.

Rebels have set their sights on the Aleppo international airport, along with the Jarrah, Kwiyres, Minnigh and Nayrab military fields. They took the Jarrah military airport on February 12.

Meanwhile, in Jaramana, a mainly Christian and Druze suburb of Damascus squarely under regime control, at least seven civilians were killed by two mortar rounds that struck near the municipality building and two schools, said the Observatory. Another 30 people were wounded, six of them critically. 

Wednesday’s violence came a day after at least 123 people were killed in violence across Syria, said the Observatory. Among them were 61 civilians, 47 rebels and 15 soldiers.

 -Reuters, MEO, TAAN, Al-Akhbar