The White House said Wednesday that it was “deeply concerned” by reports that the Syrian government fired rockets carrying chemical weapons on rebel forces near Damascus, killing hundreds of people. 

{mosads}White House spokesman Josh Earnest said the administration was “working urgently” to gather further information about the attack and strongly condemned any and all chemical weapons use. He also said the U.S. formally requested that the United Nations investigate the site of the alleged weapons use by Syrian President Bashar Assad’s forces.

“The United States urges all Syrian parties including the government and opposition, to provide immediate access to any and all sites of importance to the investigation and to ensure security for the UN investigative team,” Earnest said in a statement.

The White House also said that those responsible for chemical weapons use “must be held accountable.”

The Syrian government has denied the charges of chemical weapons use, accusing rebels of attempting to influence an ongoing U.N. investigation into whether Assad had previously ordered chemical weapons be used against his own people.

But Earnest said Wednesday that the government there must offer “immediate and unfettered access to this site” if they have “nothing to hide.”

“For the UN’s efforts to be credible, they must have immediate access to witnesses and affected individuals, and have the ability to examine and collect physical evidence without any interference or manipulation from the Syrian government,” Earnest said.

Speaking later with reporters, Earnest said the White House had “no independent confirmation” of potential chemical weapons use but was consulting with allies in the region.

He also said that administration officials on multiple levels had reached out to their allies to rally support behind a quick and thorough investigation.

“There are a number of conversations that have occurred at different levels between the United States and its allies,” Earnest said.

Earnest told reporters that while he “wouldn’t want to speculate about what may or may not have happened,” the use of chemical weapons would be “deplorable and unacceptable.”

In June, the White House said American intelligence had determined that Assad’s forces had used chemical weapons in the ongoing civil war, which has left tens of thousands of Syrians dead. The administration also announced it would begin to provide military support, in addition to the $1 billion in humanitarian aid already provided since the crisis began.

Earlier Wednesday, Sen. John McCain (R-Ariz.) said the president was to blame for the latest chemical attack after not responding more boldly following the initial determination of chemical weapons use.

“No consequence for Assad using chemical weapons & crossing red line — we shouldn’t be surprised he’s using them again,” McCain tweeted Wednesday.

Earnest admitted that so far, administration had not “attained our goal” despite an escalation of aid to the Syrian opposition, conceding that “our policy has not succeeded yet.”

“It has not resulted in the outcome we’d have liked to see, which is Assad removed from power,” Earnest said.

Earnest challenged the Assad regime to “live up to” their statements ” that they are interested in a credible investigation to get to the bottom of what exactly has happened.”

“If they actually are interested in getting to the bottom of the use of chemical weapons and whether or not that’s occurred in Syria, then they will allow the U.N. investigative team that’s already in Syria to access the site where chemical weapons may have been used, it will allow them unfettered access to eyewitnesses or even those who were affected by the weapons, it will allow them to collect physical samples without manipulation and it will also insure the security of that team as they do their work,” Earnest said.

The rebel coalition in a statement Wednesday asked the United Nations to call an emergency session on Syria.

“The Syrian Coalition emphasizes that the Security Council’s failure to assume its responsibilities towards the unfolding situation in Syria would raise questions about its raison d’être,” the group said in a statement. “If the Security Council does not act firmly, it will lose all legitimacy.”

Statement by Principal Deputy Press Secretary Josh Earnest on Allegations of Chemical Weapons Use in Syria

This report was originally published at 12:20 p.m. and last updated at 1:53 p.m.