Turkish Prime Minister Recep Tayyip Erdogan said Thursday that the Syrian regime has used chemical weapons against opposition forces, crossing the "red line" set by the administration of U.S. President Barack Obama as a precondition for more forceful American intervention in Syria’s bloody civil war.

“It is clear the regime has used chemical weapons and missiles,” said Erdogan to NBC News.

“We want the United States to assume more responsibilities and take further steps. And what sort of steps they will take, we are going to talk about this,” he added, referring to a meeting he has scheduled with Obama on May 16.

That adds the Turkish leader to a growing list of critics of the U.S. administration’s hesitance to intervene in Syria despite a growing body of evidence suggesting the regime of Syrian President Bashar al-Assad has used chemical weapons against rebel forces.

The Syrian uprising, which began in March of 2011, pits rebels -- united loosely under the banner of the Free Syrian Army -- against Assad’s well-armed military. At least 80,000 Syrians on all sides, mostly civilians, have died during the conflict, and millions have been displaced.

The U.S. administration has pledged $510 million in humanitarian aid to ease shortages of food, shelter and medical supplies in Syria and in refugee camps in neighboring countries.

Obama said in August of last year that “a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus. That would change my equation.”

Officials later told the New York Times that the statement was off-the-cuff and intended to intimidate the Syrian regime, not to draw a line in the sand to which Washington could be held accountable.

Obama is now caught in an increasingly uncomfortable situation. Washington now acknowledges the likelihood that the Syrian regime has used chemical weapons against the rebels, but remains reluctant to intervene militarily, be it with airstrikes, arming the rebels or establishing a no-fly zone over northern Syria.

Erdogan said Thursday that Turkey would support a no-fly-zone, which would make use of Turkish territory along Syria’s northern border. He also noted that his country is currently hosting about 300,000 refugees from Syria, which has cost Turkey almost $1 billion in aid money.

“There are patients who are brought to our hospitals who were wounded by these chemical weapons,” he added.