The U.S. government said Thursday that it is unable to conclusively determine that chemical weapons were used in Syria, as it is scrambling to gather all possible information on what happened in the war-torn country that reportedly killed hundreds of people.

"At this time, right now, we are unable to conclusively determine CW (chemical weapons) use, but we are focused every minute of every day since these events happened yesterday on doing everything possible within our power to nail down the facts," State Department spokeswoman Jen Psaki told a news briefing.

U.S. President Barack Obama has directed the intelligence community to "urgently gather additional information" on the alleged use of chemical weapons by Syrian government forces. "That is our focus on this end," Psaki said.

Syrian opposition charged that government forces killed 1,300 people in chemical attacks in the suburbs of Damascus Wednesday, a charge denied by the Syrian government. The allegation came just two days after a group of UN inspectors began a probe into alleged use of chemical weapons in Syria in March.

Obama has previously declared that the use of chemical weapons will be considered to be crossing "a red line" by the Syrian government, and will lead to U.S. intervention in Syria's civil war.

But the president has failed to take major actions after the Syrian government and rebel forces exchanged accusations over a chemical attack on Khan al-Asal on March 19, which killed at least 25 people and injured 130 others.

Martin Dempsey, chairman of the U.S. Joint Chiefs of Staff, has revealed that the reason the U.S. is reluctant to intervene in the Syrian civil war militarily despite its capability is that no Syrian rebel faction has so far committed to supporting the U.S. interests once it seizes power.

Meanwhile, the U.S. government is seeking coordination and cooperation from its allies and partners on investigating the alleged use of chemical weapons in Syria, Psaki said.

U.S. Secretary of State John Kerry has spoken on the phone in the past days with the opposition Syrian National Coalition leader Ahmad Jarba, UN Secretary General Ban Ki-moon, EU High Representative for Foreign Affairs Catherine Ashton, and his counterparts in France, Jordan, Qatar and Turkey.

Psaki said those calls were "part of our efforts as an administration to discuss what other countries are hearing," and Kerry will report to the U.S. national security team which has been holding meetings on Syria.