The Emir of Qatar Sheikh Tamim bin Hamad Al Thani addresses the United Nations General Assembly in the Manhattan borough of New York, U.S., September 20, 2016. REUTERS/Mike Segar

UNITED NATIONS (Reuters) - Qatar’s emir criticized U.S. President Barack Obama’s policy on Syria on Tuesday, highlighting the growing frustration among U.S. allies at what they perceive to be Washington’s lackluster action towards the protracted civil war.

Qatar, home to a U.S. base, is a vocal critic of Syrian President Bashar al-Assad and, like the United States, has supported rebels seeking to topple Assad.

Speaking to the United Nations General Assembly, Sheikh Tamim bin Hamad al-Thani, criticized Obama’s so-called “red line” on Syria.

In August 2013, Obama abruptly canceled plans for U.S. air strikes that he had vowed to order if Assad’s forces crossed a “red line” and used chemical weapons. Nine days earlier, a Sarin gas attack killed as many as 1,400 Syrians.

“Red lines were set for the regime who has violated them, yet those who demarcated those lines have not felt provoked to raise a finger,” Tamim said according to an English transcript of his prepared remarks.

“The red line continued to be shifted until the regime became aware of the fact that there is no ceiling for what it could perpetrate without accountability,” Tamim said.

Obama’s Syria policy has been predicated on the goal of avoiding deeper military entanglements in the chaotic Middle East. Critics accuse Obama of being hesitant and risk averse. Obama’s limited intervention has focused on fighting Islamic State militants who control a swath of Syria and Iraq and which has inspired attacks in the United States.