U.S. President Barack Obama has said the United States has evidence that chemical weapons have been used in Syria but not enough facts yet to initiate a response.
"What we now have is evidence that chemical weapons have been used inside of Syria, but we don't know how they were used, when they were used, who used them," Obama told a White House press conference.
He repeated his previous statement that the use of chemical weapons would be "a game changer" but said any decision to react must be based on "the facts."
"If we end up rushing to judgment without hard, effective evidence, then we can find ourselves in the position where we can't mobilize the international community to support what we do," Obama said. "There may be objections even among some people in the region who are sympathetic with the opposition if we take action."
Obama said he has asked the Pentagon to draw up "a spectrum of options" if it is established that Syrian President Bashar al-Assad’s regime has used chemical weapons on civilians. He said there are options “on the shelf” that have not been used so far but might be if the evidence is incontrovertible.
Syria's UN ambassador Bashar Ja'afari on April repeated calls by his government for the UN to send experts -- now assembled and waiting in Cyprus -- to investigate its claims the rebels used chemical weapons in Aleppo.
"The Syrian government is still willing to receive the investigation team in even less than 24 hours."
The Syrian government and the opposition blame each other for alleged chemical weapons attacks in Aleppo in March and another such attack in Homs in December.
Syria wants the UN team to probe only the Aleppo attack, but UN Secretary General Ban Ki-moon wants the inquiry to cover both incidents. That disagreement is holding up the team in Cyprus.
Ja'afari also singled out the United States and Britain as countries trying to smear the Damascus government.
"The Syrian government has always emphasized in Damascus as well as in here that it will not use if it possesses any chemical weapons against its own people."
One of the themes that came up was the recent bombing of the Boston Marathon, which killed three people and injured hundreds more.
In response to a question on whether U.S. intelligence agencies were at fault for failing to prevent the April 15 twin bombings, Obama said he believed the FBI and Department of Homeland Security “did what it was supposed to be doing.”
Two Russian immigrants, Tamarlan and Dzhokar Tsarnaev, are alleged to have carried out the attack. Obama said Russian President Vladimir Putin had assured him of Moscow’s full cooperation with the U.S. investigation into the men’s backgrounds in the United States and Russia.
"The Russians have been very cooperative with us since the Boston bombing," Obama said. "Obviously, old habits die hard. There are still suspicions sometimes between our intelligence and law-enforcement agencies that date back 10, 20, 30 years, back to the Cold War. But they're continually improving."
Obama also addressed the growing hunger strike at the Guantanamo Bay prison for terror detainees, which the military now says involves 100 of the 166 remaining inmates.
He said he did not want “these individuals to die” and said he would “reengage with Congress” on the future of the detention center, which blocked his attempts to close it in his first term.
"Guantanamo is not necessary to keep America safe," Obama said. "It is expensive. It is inefficient. It hurts us in terms of our international standing. It lessens cooperation with our allies on counterterrorism efforts. It is a recruitment tool for extremists. It needs to be closed."