DAMASCUS, Syria — The U.S. ambassador to the United Nations said Sunday that reports of a poison gas attack in a rural village north of Damascus were so far “unsubstantiated,” adding that the United States was trying to establish what really happened before it considers a response.

Both sides in Syria’s civil war blamed each other for the alleged attack that reportedly injured scores of people Friday amid an ongoing international effort to rid the country of chemical weapons.

The details of what happened in Kfar Zeita, an opposition-held village in Hama province, remain murky. Online videos posted by rebel activists showed pale-faced men, women and children gasping for breath at what appeared to be a field hospital. They suggested an affliction by some kind of poison – and yet another clouded incident where both sides blame each other in a conflict that activists say has killed more than 150,000 people with no end in sight.

“We are trying to run this down,” said Samantha Power, the U.S. ambassador to the United Nations, during an appearance Sunday on ABC’s “This Week.”

“So far it’s unsubstantiated, but we’ve shown, I think, in the past that we will do everything in our power to establish what has happened and then consider possible steps in response,” she said.

In the Syrian capital, Syrian President Bashar Assad said the conflict in Syria was shifting in the government’s favor.

“This is a turning point in the crisis, both militarily in terms of the army’s continuous achievements in the war against terror or socially in terms of national reconciliation and growing awareness of the true aims of the attack on the country,” state-run Syrian television quoted Assad as saying.