The US government said Wednesday that there was no "credible evidence" so far that showed the Syrian government forces had used chemical weapons.

"At the time we looked into the allegations that were made and the information that we had received, and we found no credible evidence to corroborate or to confirm that chemical weapons were used," State Department spokeswoman Victoria Nuland said at a daily briefing.

Nuland's statement came after the Foreign Policy magazine reported on its website Tuesday that a secret diplomatic cable from the US consulate in Istanbul, Turkey, had concluded that the Syrian government had probably used chemical weapons.

While admitting the existence of such message from the Istanbul consulate, Nuland told reporters that the State Department had concluded that the report cannot be corroborated.

However, the spokeswoman reiterated the Obama administration's harsh warning against the use of chemical weapons in Syria.

"We have been absolutely consistent and clear, from the president on down, that our red line is: we have a red line with regard to use of chemical weapons or their proliferation," Nuland said.

"If the Assad regime makes the tragic mistake of using chemical weapons or fails to meet its obligations to secure them, there will be consequences, and the regime will be held accountable," she added.

On Dec. 3, in a speech at the National Defense University in Washington, D. C., US President Barack Obama warned Syrian President Bashar al-Assad of "consequences" in using chemical weapons in the Arab country's lengthy conflict.

"The use of chemical weapons is and would be totally unacceptable, and if you make the tragic mistake of using these weapons there will be consequences and you will be held accountable," he said at the time.