WASHINGTON, May 16 (UPI) -- U.S. President Obama Thursday again said more investigation is needed to determine whether the Assad regime in Syria has used poison gas on rebels.
Obama appeared at a joint White House news conference with Turkish Prime Minister Recep Tayyip Erdogan, who has been pressing the administration to take a stronger stand in Syria.
"It is important for us to get more specific information about what is happening" in Syria, Obama said.
"But what's going on now by itself is strong enough to prompt international action," such as sanctions and other pressure, Obama said. "I preserve the options of taking additional steps both diplomatic and military ... but this is also an international problem."
The president said he and Erdogan "both agree [Syrian President Bashar] Assad has to go."
Obama said he and Erdogan also agreed it is critical that Iran not acquire a nuclear weapon.
Erdogan called for cooperation on Syria and closer economic ties with the United States.
Before leaving Ankara, Erdogan said he planned to present evidence at the White House meeting with Obama and Vice President Joe Biden of Syrian chemical weapons use to strengthen his case.
Obama has said proof of chemical weapons use by Assad's forces would be a "red line" and a "game-changer," but has so far said the evidence of such use was insufficient to prompt U.S. action or enable him to unite U.S. allies behind such a response.
Turkey has NATO's second-largest army.