Kerry: Chemical use a 'moral obscenity'
- The White House believes Syria's government is behind the chemical attack
- Obama is considering options for responding to Syrian chemical attack
- Source: Ground troops or no-fly zone ruled out for now
- Cruise missiles are the most likely option to punish the Syrian regime
Washington (CNN) -- Few question that there was a major chemical attack in Syria last week, and the United States has made clear that it blames the government of President Bashar al-Assad.
Now, the question is how President Barack Obama will respond.
For almost two years, Obama has avoided direct military involvement in Syria's civil war, only escalating aid to rebel fighters in June after suspected smaller-scale chemical weapons attacks by Syrian government forces.
However, last week's attack on a Damascus suburb that reportedly killed and wounded more than 3,000 people obliterated the "red line" Obama set just over a year ago against the use of Syria's chemical weapons stocks.
At the White House, spokesman Jay Carney told reporters Monday that Obama was evaluating "a response to the clear use on a mass scale with repugnant results of chemical weapons," adding that "there is very little doubt that the Syrian regime ... used those weapons."
Meanwhile, U.S. Secretary of State John Kerry called the attack "inexcusable" and "undeniable," and said there was "a clear reason that the world has banned entirely chemical weapons."
He said that evidence "strongly indicates" chemical weapons were used in Syria and that "we know the Syrian regime maintains custody" of such weapons and has the rockets to use them.
Read Kerry's remarks
Obama "will be making an informed decision about how to respond to this indiscriminate use" of chemical weapons, Kerry added, saying the president "believes there must be accountability" for those who use them.
Options available to Obama range from ordering limited missile strikes to continued diplomatic efforts labeled by critics as a "do-nothing" approach.
Earlier Monday, a White House official ruled out sending soldiers to Syria or implementing a no-fly zone to blunt al-Assad's aerial superiority over rebels fighting to oust his regime. The official insisted that all other options were under consideration by Obama but put no time frame on a decision.
Meanwhile, a senior Defense Department official told CNN's Chris Lawrence Monday that four U.S. Navy destroyers "maintain readiness and, if required, could execute a mission within hours" of being ordered to do so.
But the official added that the U.S. military reamined "in a holding pattern" as Obama considers both military and nonmilitary options.
Also, Defense Secretary Chuck Hagel said while visiting Indonesia that any U.S. action "will be in concert with the international community and within the framework of legal justification."