The United States refused to set new "red lines" for Syria Wednesday as claims of a horrific chemical arms strike reignited debate over Washington’s reluctance to intervene in the civil war.

The United States refused to set new "red lines" for Syria Wednesday as claims of a horrific chemical arms strike reignited debate over Washington's reluctance to intervene in the civil war.

But the top US military officer, General Martin Dempsey, pushed back on calls for air strikes, which he said could embroil America in an open-ended war.

The new claim of chemical warfare lured Barack Obama's administration onto difficult political ground after the president was accused earlier this year of not enforcing "red lines" he set over such attacks.

"I'm not talking about red lines. I'm not having a debate or conversation about red lines ... I'm not setting red lines," said State Department spokeswoman Jen Psaki.

The White House meanwhile refused to specify what, if any action Assad would face if it was proven that his forces were behind the attack in which many victims apparently choked to death.

Spokesman Josh Earnest focused instead on a team of United Nations inspectors in Syria to probe previous claims of chemical attacks, saying they should be allowed to examine the new alleged incident.

"Before we suggest what may or may not happen as a result of the investigation's findings being revealed, let's start with making sure that this investigation actually gets conducted in a manner that is credible," he said.

A year ago, Obama said at a White House press conference that any use of Assad's deadly chemical arsenal would cross a "red line" and would entail "enormous consequences."