POTUS insists that US is investigating reports of attacks, but implies that chlorine may not justify action against Syria.

Widespread reports of chlorine gas attacks in Syria have not been prevented - or acted upon - because chlorine is not "historically" considered a chemical weapon, US President Barack Obama stated Thursday.

Obama was forced to answer the chlorine question during a press conference from a summit at Camp David with leaders of the Gulf states. Syria and Iran were key issues at the conference.

However, when pressed about chlorine, Obama evaded defining it as a "weapon," noting that it has many other non-threatening uses, as caught in this footage from the Washington Free Beacon.

"Chlorine itself is not listed as a chemical weapon," he insisted, referring to the US's pledge against chemical weapons use in Syria.

In his response, Obama made reference to the Organization for Prohibition of Chemical Weapons (OPCW), which indeed supervised the liquidation of Syria's sarin gas over a year-long process that ended in late 2014.

However, the chemical watchdog indeed concluded in January "with a high degree of confidence" that chlorine gas had been used in attacks on three villages in Syria last year.

Both UN and US officials have said that they are investigating the claims.

"There is mounting evidence of repeated use of chlorine" in Syria, a United Nations Security Council diplomat said to AFP last week. "There is a proposal for a mechanism which would allow relevant experts to have the right kind of access to answer the questions about attribution."

"We are actively engaged in conversations with UN colleagues regarding the continued use of chlorine as a weapon in Syria," a US official added. "The Security Council must address the need to determine who is responsible for using chlorine chemicals as weapons in Syria."

Photos have surfaced just this week exposing at least one major chemical attack - if not several - in the Syrian province of Idlib.

Gil Ronen contributed to this report.